Pyke is the most agressive, stressful support you can possibly play. If you commit to it and make it your main, well congratulation, you work well under pressure.
Pyke is a CC but also an escape artist. When you build him for it, you can catch up with ANYONE in order to secure kills. Make sure not to put yourself in awkward positions though!

P - Your passive is what gives you sustain in lane. Although you're not a tanky character at all, this passive allows you to take a hit or two and live with it just fine. Combo with your W that makes you invisible to get out of sight and start regenerating. This passive also makes it impossible for you to gain extra max health and converts it to AD instead.

Q - Your Q is your bread and butter. This is the first aspect that you have to master as a Pyke main - Landing those Q. If you can land a couple of them early game, you give some serious chances to get early kills and snowball from there. Be careful not to get an enemy closer when you or your ally are low hp - it could kill you. When you help a friend that is running away, make sure you pull the enemy in another direction.

W - Although its the last ability you boost, your W is insanely important - you gain some movement speed and become invisible to the enemy if you keep a certain distance. It allows you to engage while surprising the enemy but also to run away when things get ugly. You can easily combine this with your E or your R.

E - This is the second hard thing to master as a Pyke - your dash. Dashing through one enemy is fine, dashing through 3 is magnificent - because it will stun them all. When you combo it with your Prowler's Claw and the stars align just a little, you can stun an entire team. Be careful though - you're still targetable as you dash towards someone - so dont think that you can outplay a lux or a morgana without having the chance to get a Q right in the face.

R - Your ultimate is what makes Pyke a menace. It will execute any enemy who's health is below a certain point (when the enemy's life bar is red) Increase your lethality to be able to execute even when the enemy still have a reasonable amount of HP! If you land an ult, you'll have a rather long cooldown that will allow you to ult again - the cooldown will reset if you get another kill. It goes on like that infinitely, so if you play your cards right, you can easily get a pentakill. Also, if many low-health enemies are on the same spot, you can execute them all in a single strike.

Pyke is extremely strong starting level 2.
You hook, dash, stun and exaust your opponent and watch your adc finish the job. Hail of blades even allows you to secure one or two solo kills depending on the matchup! Pyke can invade other lanes too but be careful to not abandon your own. When the jungler does first drag, go mostly to help if ever the objective is contested.

Pyke will fall off mid game if you're not careful. By the time you're building your axiom arc, you have to start thinking like an assassin. Dont make plays all by yourself, try to get involved into other plays or to set up something for your nearby teamates. Dont forget that even out of your lane, you're still a support.

Creating an engage can be dangerous at that point - one stun can be fatal for you. Make sure you hook when the entire enemy team is not gonna fall on you afterwards. Best you can do most of the time is to taunt the enemy into engaging - then you escape, help your team a bit and when their hp is low, you start ulting everything. In late game, if you play well, you will get your beloved pentas. Also, this is usualy when Edge Of Night really comes in handy - it saves you from this deadly stun that marks the beginning of your 50 seconds penalty on the bench.