This build/guide is still in progress.
The aim of this build is to reinforce or enhance sky’s strength and cover/compensate for its weakness.

Strength:
Spammable skills - Arcane Bolt (Q) has low cooldown and low mana cost, after 2-3 auto attack you can cast Q again. This is good for Harassing, finishing of or chasing down enemies.
Long range attack for ganking - Concusive Shot (W) is your slow, it has a insane range you can cast it while out of enemy sight then follow-up with your combo, most of sky’s skill has a long range
High damage ulti - Mystic Flare (R) is an AOE attack it has a high damage
Great Combos on skills - sky has slow, silence that amplifies magical damage, a high damage burst attack and a spammable skill.

Weakness:
Low base damage
Low armor
Needs to snowball your skills and items in order to be effective
Weak late game - sky can be countered with BKB, vanguard etc making late game hard.

Your high burst damage combo:
Start with your slow (concussive shot) then use your silence which amplifies magical damage then hit with your Ulti usually this will be enough if not chase finish off by spamming your arcane bolt (1-2 arcane bolt plus physical attack would usually do the trick).
Getting your slow and silence to hit almost at the same time makes your opponent very vulnerable.
Tip:
• If possible ensure that the first two spells you will be casting will almost simultaneously hit the enemy.
• Concussive shot has a insane range on ganks hide out of sight use concussive then pop out of cover and use your combo.
• Lead your Ulti, meaning anticipate where your enemy will be moving to then adjust where you will place your Ulti

Early Game:
Sky is most effective solo mid lane but can be used on any other lane. Early on harass the enemy to get their health low and to push them back in order secure last hits or keeping them off your carry then when the opportunity presents itself get the solo or coordinated kill.
The starting items were chosen to keep sky on the lane longer, spam arcane bolt, and survive early encounters.
Once you get your Ulti or even before, you can setup with your teammate ganks.

Mid Game:
Start ganking and roaming if possible don’t initiate fight stay behind your team in team fights. Isolate an enemy then finish him off with your burst damage.
Around this time you might be going back to base a lot as your combo takes a lot of your mana pool. This is why it’s more crucial that you get your items.

Late Game:
This is where sky is least effective as your enemies would already have counters for you like getting BKB, vanguard or generally is watching out for you.
Hopefully by this time you already have your items that would help you setup your attacks.