What you need to aim at is to harras as much as posible with your Q. Your baisic and most powerfull combo is ...

Try to land as much as possible of Q before using W, then use E and Q's again. (You get 100% from your E spell) which means that you will crit not form E but from everything, that is why your you have 15% HP pantheon can one shot you)

When using your ult try to aim it that way so you will block your enemies escape. This will garantie you a successful gang and kill because with pantheons passive you can easily dive under tower. ( Remember that while in your ult, before you land , use your W on the target that is in the circle, this will stun him upon your arrival.

The rest is up to you summoner. Good luck on the battle field.