Update: This guide was written for a much older version of the game. Most of it still applies, but certain things (like Deathwish, grenades, camping as a sniper) are not covered. I might update it eventually, but for now, it's still an effective guideline, and it will definitely help make you a better PD2 player who gets to play more than he gets kicked!
Well, we've all been there; you just got kicked from a public game, and you're not quite sure why. It's quite a pain when you can't figure it out. Hopefully this will give you some ways to prevent this in the future! Now, let me state this clearly: Some people will kick without reason or explanation. It sucks, but you can't really help that. On the other hand, it's also difficult for a host to kick the very instant you mess up sometimes, so you might get booted when they finally get a chance. It's usually best not to immediately assume the host was a random jerk; he simply may have been pretty busy smashing up some Tasers.
Now, for those kicks that were, in some way, warranted; here's a few guidelines to prevent it from happening, and make you a more valuable teammate in the process!
Whether it's text or voice, try and be helpful and responsive. You don't have to joke around the whole mission or cheer every time someone shoots a shield, but if you're in loadout, and someone's asking you to switch back to your previously equipped C4, it's sort of rude to just equip a medic bag, ready up and remain silent. Now, in order to get comms down, try and communicate what's needed only. "Guard backdoor", "saiga", "I got Inspire aced"; they're basic things that don't take forever to type out. Better yet, you can use a microphone, but there's up- and downsides to that one.
The use of a mic will, generally, make your communications more efficient. However, if you're using a mic, there's a few things to keep in mind:
Use Push-to-Talk. Nobody wants to hear your heavy breathing.
Don't yell at others.
If you're frustrated, probably best not to use it.
Don't go on endless, unrelated rants.
Don't cut people off.
Try to remember not everyone is mic-equipped.
Check your setup; don't have speakers looping sound over your mic.
Also; for the sake of teamplay, don't mute voice chat by default. Mute annoying individuals or just wait for a host to kick them.
Now that we went over communication, let's have a look at gameplay basics. Step 1 might simply be to select what difficulty level you're going to be playing at. If you just bought your first rifle at level 5, chances are you're not going to be very valuable yet in any Overkill heist, let alone a Pro Job. Leave those be for now. In fact, you'll usually want to have played the heist a few times at Hard or Very Hard before you dive into Overkill. There's a pretty big gap in combat difficulty there, so knowing the maps shouldn't have to be an extra issue.
When it comes to map specifics, there's actually quite a bit to learn in Payday 2. From knowing the way to pick the right engine on Big Oil, to understanding that on Watchdogs Day 1, the car will arrive after you throw in the first 4 bags - and thus, you should get all bags ready to throw first. Of course, these things by themselves won't often be reason for a kick, but it adds up. All in all, it really pays to get the maps down on the lower dificulties - games are a lot more forgiving there. But understand that if you ran out of the bank with a bag of gold and barely made it to the van, you probably won't make that same distance on Overkill. On a small side note; Normal Jewelry Store is a bit of an exception here. Speedrunning is a common way to grind for cards, and if you lag behind, you'll get escorted out before the 1 minute mark.
Now let's say you understand how to do these Bank Heists by now - you join an Overkill lobby, and notice everyone else is in suits and has ECMs equipped. It's a dead giveaway that it's a stealth run, and if you're not familiar with that, that's usually fine. Most people I know don't mind a non-stealth player sitting in on their stealth runs - but try to stay out of the way. If you're following around someone sneaking past a guard, while you're wearing 75 Visibility gear.. chances are it's not gonna be appreciated. Try to observe (and ask) rather then jump in if you don't know what's going on. As an example, I'll often run ECM rushes on Firestarter Day 2 with people unfamiliar to the concept. As long as you either stick to the spawn, or go directly for the evidence room and don't shoot anyone, you're working towards the team goal despite not being familiar with the strategy.
Lastly - and this is a major point for a lot of hosts - try to be a team player. If your buddy runs past a Shield and the Shield turns - pop that sucker! Drill broken and you're close to it - fix it (this is something even experienced players have trouble doing, sometimes ;))! Not sure what the hell to do? Ask. If there's nothing particular to do but fight off cops, do that. Make sure to watch your armor and ammo levels, stay within reasonable distance of your teammates, and mark any special opponents!
Some things though, just become a nuisance. And it starts with your name. If your Steam handle is Adolf_KillTheJews666, you can expect to see the "you've been kicked" message a lot. Not just the name, though, obviously; being bothersome, offensive or rude to your fellow players is a sure way to get booted frequently. I know, I know, it's the internet, but try and be nice to people. Similarly, don't accuse others of hacking or exploiting if you're not 100% certain. It's bad manners, and often just goes to show you're not very familiar with the game yet.
There's plenty of other things that cause you to be annoying to others though. Picking up instant cash when you don't have Dead Presidents aced, but another person does? Breaking camera's on a stealth run without letting others know? Shooting the guy your teammate is trying to convert? It's all pretty damn annoying. Another pretty big one is when after a succesful heist, someone goes back into the level to bring a body bag to the van. It's such a waste of everybody's time.
Actually, there's a lot of things that involve your teammates that can annoy them without you realizing it. Mostly, the 'doubling up' effect can be a bit tedious after a while. If you're the second person to start repairing the drill, it's better to drop the repair and cover your teammate instead. See a teammate headin towards a weapons case? Go for another one. Same thing for revives - unless you have Inspire aced, but please, announce that before readying up!
A final note here on the efficiency of the ammo and medic bags. On a combat-heavy mission (such as a 7 bag cook on Rats), make use of the assets as little as possible. Typically, if you haven't gone down 3 times yet (when your screen goes greyscale), you don't need to use that medic bag yet. 'Topping off' your health is just a way of making your teammates hit custody faster. Ammo? Same thing - try to be as efficient as possible, lasting long times between needing to reach for an ammo bag. If you're finding that impossible, it might be time switching weapons or improving your aim a little.
In the end, though, it all comes down to the host. It's always good to acknowledge that; he eventually has the final call. So if you're in a game where the host says "Hey, let's stealth this" and you run in mowing down everyone you see with a loud weapon, chances are you're getting kicked. Just respect the host's wishes, and if you can't bring yourself to do that; leave. It's better for both sides involved. Of course, sometimes a host might want to make room for a friend; I encourage any host to wait until the end of the mission, but in the end, it's their prerogative. Luckily, most hosts will let you know why you're kicked in instances like this!
Another point to mention there, is that usually, a host's say is final. If you're really wanting to stealth that heist, but the host wants to go in guns blazing, arguing is usually not going to help. Either you gear up and do it, or leave and find a different lobby where they are, in fact, trying to stealth. Don't go and argue, and definitely don't just gear for what you want to play despite being asked not to.
If you're running into a lot of bad hosts, though, you can always host yourself or join a friend's game. Just try to be the best host you can, so others don't run into the same wall you did. Friendliness goes a long way.
So let's sum this all up in a few key guidelines:
Understand the game
It's quite brief, of course, but it's what it comes down to. Apply a little bit of courtesy and a little bit of common sense, and you shouldn't be having too many issues. Hopefully, this all helps to let you enjoy the game a bit more! It might not entirely prevent you from being kicked, but it should be a good start. Happy fraggin'!