Pretty straight on.. Use your E on minions from safe distance to bounce on prefarable the enemy adc. Only directhit enemies with E if you can do it without risk of being all-ined. Goal is to deal some dmg and farm gold. Be careful to not steal your adcs cs as it slows your income on spellthiefs. Take 2 or 3 points in E depending on what you wanna achieve. Be sure to ward the river and save mana for Q if you get ganked. Always Q the adc or jungler if your adc becomes cc'ed.

As soon as you hit lvl 6 you wanna look for roams mid with your ult if you cant get a good ult on your own lane. This is also why you rush mobilityboots before zhonya.

At this stage you wanna play around your ult. With Ult/Ignite you can 1v1 squishes and make alot of dmg in teamfights. Roam the map to look for kills/assists, but dont walk in unwarded jungles if you dont know where enemyjungler is.
In teamfights you ult in and pop your zhonya after you feared someone (if u get focused) If your ult is down play it safe and make sure to Q threats to your carry and silence them with your E


also
*Ward next upcoming objective (drake/baron) and also keep rivers warded.
*carry a controlward to put down if you are hiding and looking to ult and not sure if its warded.