In lane you want to poke, and poke and poke, the enemy adc should be about half life all the time.
Your level 1 and 2 are good, but after level 3 try to play defensiv untill you reach level 6. When you get that lvl 6 try to get a fight or roam to catch the jungler doing crab.
Remember to ult last, first Q-E-W then R.
Always use your wards to look for enemys around the botside jungle, your ultimate is a extreamly dangerous weapon against solo`s.
Controll wards are important because you need to get surpirse ulties on some people, for instance a tristana can jump out of your ult range.

Late game:
-Right before a teamfight breaks out in a lane with minions close by, you can E one of them while your team is clearing them, so the virus will eventually end up on one of the enemysl.
-Because you are the support, enemys will underestimate your damage, you can use this to your advantage, for instance when you are baiting. I often pretend to clear a ward when I see a enemy sneaking up on me (which I know I can onehsot), in the moment they get into my range I turn on them. Note that you need to be 100% sure you can kill them, otherwise you will die.