The way I like to play him is as a hybrid, although mostly AP champion. All of his moves stack with Ability Power, so it only makes sense to build it on him. However, he is an auto-attacker as well, so some AD is definitely necessary, and I think that's why pure AP builds don't work very well.

For Marks I use Magic pen but as an alternative you can your Armor pen or Attack speed It dupends on player preference

For seals I use Dodge runes for Obvious reasons Dodge seal are a must

And for Glyphs I use flat AP because all of his abilities use AP

Exhaust: This makes it impossible for another melee character to 1v1 you, and makes it a lot easier to catch up to people when they start to run away.

Ghost: Makes it easier to close the gap for that extra Leap or for running away this has Saved my life countless times and Gotten me kills countless times.

Flash: can be used almost the same way as ghost except flash can jump you through walls and can be equally good.

Ignite: For those of you that like to light things on fire this goes very well because sometimes your target is close to death but by a tower you leap strike in ignite and run.

Pros:
-Great early game harassment
-Great mid-end game damage and durability
-Can be a Ad focused char, hybris focused char, or Ap focused char
-Has an AoE stun
-You can focus more on getting nice Damage and some resistances while still haveing a nice amount of health thanks to his passive
Cons:
-If he doesnt dodge he loses a vital spell
-Usually gets focused :(

My skill sequence goes as follows Empower(W) - Leap strike(Q) - Counter strike(E)[If you've dodged recently]

My best advice is to pick of squishies in team fight and try not to be the initiator you are an assassin you should be leaping out of bushes and things like that.