How to play necrons

How to play the Necrons (From a non-professional Necron player)
If you feel anything is missing, comment and lmk.

Early game

What you gotta do as Necrons early game is to build 2 warrior squads, then a Scarab squad. What you then do is use your Necron warriors to guard the Scarabs (I'd recommend reinforcing them) as they capture requisition points. While this is going on, you should build more Scarab squads and use them to build things such as generators, listening posts on captured points, and of course the summoning core. You should also make more warriors and your Necron overlord, as he is one of the better melee units available to the Necrons.

Mid game

By now, you should (hopefully) have a T2 monolith (The first upgrade) or maybe even a T3 (The second upgrade). If not, then use your warriors, wraiths and other Necron units to start pushing the enemy if you haven't already, then capture more points and put obelisks on them, upgrade your obelisks and make sure to keep a tight defense on them. Build your greater summoning core (If you haven't already) and upgrade your monolith. This should allow you to get some of your better units. Also make sure to have the forbidden archive built as this will allow your necron overlord to become much stronger, with some abilities being rather overpowered. Now play defensively-ish, transfer from offensive to defensive so you can focus on base infrastructure and building up a force. Make sure all your units are reinforced but also have a lot of power stockpiled just in-case.

Late game

If the game has proceeded this far, build an energy core. You should have a very strong army by now, so you could finish the match whenever, if the enemy isn't too strong that is. Anyway, now that you have the energy core, max out your monolith so it can move, this is one of the strongest Necron units (?) as it has a lot of HP, but if it dies and you don't have a backup, you'll lose. The energy core also allows you to research the strongest Necron lord ability, the essence of the Night-bringer, which turns the Necron overlord into the Night-bringer temporarily. The Night-bringer is a massive, hp-stealing, scythe swinging, overpowered basically mini-boss unit, he's invulnerable in this state and will shred everything, even relic units. Unfortunately, I believe it costs a relic to research.

How to fight space marines

Space marines are the most balanced faction in the game, they have access to some pretty solid weapon upgrades, including plasma guns. Plasma guns are effective against heavy infantry so they'll be a pretty solid threat in the early game, I still recommend point rushing so you can get as many things down as you can in a short period of time, as they only get stronger from here. Their hero, the force commander, is very dangerous in melee, so taking him out from range is recommended. In the mid game, they'll have access to things like apothecaries and a librarian, along with Chaplains. They'll also have vehicles like the Land speeder. The Chaplain is a melee specialist secondary commander unit, who can break enemy units with an ability and buffs nearby infantry. The apothecaries increase hp regeneration of nearby squads and have bolt pistols and the iconic apothecary drill. Librarians are psychic-melee secondary commanders that can make nearby units not take damage, the librarian still takes damage though. He can also do serious damage with some of his abilities, so targeting him is recommended. In the late game, Space marines will have the orbital relay and the predator tank. The orbital relay allows the Force commander to use his orbital bombardment ability, which will shred infantry in the blast. It also allows the summoning of 2 terminator squads, the assault squad, a melee focused variant, and a normal terminator squad. Both are very powerful units that should be treated with caution. The relay also allows the drop podding of normal space marine squads and both varieties of dreadnought. They'll also have their land raider, a very powerful gunship/transport vehicle that is the only vehicle that transports terminators. It has a lot of firepower so it should be targeted over everything else. They will have access to a single artillery vehicle as well, more of a support kind over proper DPS vehicle, it is capped at 1 active at a time and is very quick, has good HP and solid accuracy, but lacks good DPS on it's own. If you feel ready to attack at this point, go ahead.
Notes: This was written before I formatted it and I am NOT trying to do that again.
The sergeant they get, which is a squad upgrade, has an ability that instantly restores morale to the squad.

How to fight the Eldar

Early game, they're very vulnerable, so rushing them or point rushing should do pretty good against them.
Mid-game, they're really annoying, so take them out then.
Late-game, they are the embodiment of pain and suffering, kill them before it's too late.
This is less detailed because god-forbid I enjoy fighting Eldar, it's so boring.

How to fight the Tau

The Tau are quite annoying to fight, most of their units go infiltrated, the Necrons lack detector units. Luckily, the Tau have quite possibly the worst DPS i've ever seen unless they're using late game units.
Early-game, you'll want to take them out here as they only get more annoying from here.
Mid-game, they get very powerful, infantry shredding vehicles and lots of heavy hitting infiltrated units.
Late-game, they get SUPER DUPER powerful, insanely strong vehicles and units, such as the greater knarloc, their relic unit, which isn't very good. But it's good enough as a distraction, to let the rest of their vehicles and heavy hitting units to move in.
Of course this is less detailed because like before, I hate fighting the Tau because it is simply tedious and boring. Therefore I have less information.

How to fight the Imperial Guard

The IG are a swarming faction, dedicated mostly to swarming enemies with their overwhelming, loyal infantry. Commissars are the one thing keeping their morale high, so if they fall, the guard falls. Guardsmen lack anti-heavy infantry weaponry for their infantry. Most of their anti-heavy infantry comes from Ogryns, Kasrkins and the Vindicare, of which all are ranged besides Ogryns, who shoot then go into melee. Their vehicles are most of their firepower and should be a force to reckoned with, so target the strongest vehicles if you can. If you see a baneblade, you should advance with EXTREME caution, as that can and WILL shred everything you throw at it until it falls. They can teleport infantry through buildings so be careful.

Early-game: The guard are weak and vulnerable to a warrior rush, although that's the boring way to end a fight. They barely have any units, limited to basic guardsmen, their command squad, adeptus mechanicus (Who can fight), and heavy bolter turrets. And perhaps commissars along with heavy weapon squads. Attack now or keep preparing for late-game.
Mid-game: The guard are now getting stronger, having priests, psykers, upgrades on their infantry, basic vehicles (The chimera, sentinel, etc.) and have Kasrkins, Ogryns, and a pretty solid army up. It will be harder to take them down by now as they can reasonably fight off a solid Necron force. They also have Sergeants, a morale-boosting unit without any unique abilities, they are a squad upgrade.
Late-game: The guard is at its peak, they have all the vehicles unlocked, including basillisks (The absolutely OP artillery, the one with the earthshaker round, you know the one.), the hellhound, and the fabled baneblade. They will have a very powerful army, a solid infrastructure, and enough resources for the longest battle of attrition you'll see. If they aren't dead by now, kill them before they decide to attack.

How to fight da biggest, baddest orky horde.

The orks are a very strong, swarm based faction with a very powerful relic unit, along with some vehicles on the side. They have solid infantry, powerful hero units, and very strong abilities. They are weighed down by their unique, ork faction only resource, which makes them particularly vulnerable in the early game.

Early game: The Orks are vulnerable, although they have strong infantry so a large force of warriors would be advised for an early game rush. They have shoota boyz and slugga boyz, along with their commander, who is very deadly in melee, along with a sub commander who can teleport and is also deadly in melee.
Mid-game: The Orks now have access to a lot of ork pop, and most of their units, so they should be taken down by now, if you can that is. They are pretty strong by now unfortunately, so be careful.
Late-game: If the Orks aren't dead by now, it's going to be pretty difficult, they should have a very large army and vehicles, a lot of them, and their relic unit. The relic unit is a transport-tank, it's a very large creature that will shred nearby infantry, so fight from range. It also has a stampede ability, where it charges forward, destroying most of the things in its path.

How to fight the Chaos

The chaos are sort of like the marines, except with less morale, more hp, they're cheaper, and they lack the immediate availability of plasma guns. Instead, they get demons, a very powerful artillery cannon, and the 'Ultimate melee unit', along with the strongest (In my opinion) character in the game.

Early game: The Chaos have cultists and marines, along with raptors, the Chaos have low morale so breaking them should be easy, but they are pretty strong. The Chaos lord can go toe-to-toe with all the other commanders in melee and usually win, due to his high health and high damage. Use warriors to fight off most early game attacks as the Chaos tend to play half-attrition (At least against AI.)

Mid game: The Chaos have horror squads, most of their infantry, and the Chaos sorcerer, they also have vehicles and access to plasma guns. The Chaos sorcerer is a very powerful unit from range, and still strong in melee, he's like a librarian, except his spells are more DPS focused rather than being a support unit. The defiler, the Chaos artillery, will be ready to shred your infantry in both melee and at range. The Chaos lord falls off here as his HP just isn't high enough to make up for his low movement speed. Better units are recommended here along with lots of warriors for defiler bait. They now also have Champions, which increase DPS of squads with their ability, and are also vessels for the Blood-Thirster.

Late game: The Chaos have reached their peak, they now have all their vehicles and infantry. The Chaos lord makes his comeback here, ready to kill other commanders once again, and slaughter infantry. He's got more HP, more morale, and if they have a sacrificial circle, can now become a daemon prince. As a daemon prince, he's stronger, faster, better in every way, he is now his ultimate form. Unfortunately, he cannot attach to squads and will detach from the one he was connected to. They can now also summon The Great Blood-thirster, the strongest unit in the game. The Blood-Thirster can scare units off with a roar, breaking them instantly, heals in melee, has several AOE abilities, his attacks hit many units, and he's got such high HP even a dark souls boss could be jealous. They now also have access to possessed marines, the 'Ultimate melee unit' as the game calls them, the squad has a limit of 8, they can be upgraded to breathe fire which does lots of damage and shreds morale. They hit like a truck in melee and are generally used as half shock-troopers half DPS machine. Throw everything you have at the Blood-Thirster should he be summoned.