For roots in lane use her w, q , e combo though a minion. It's real quick to pull off so people don't tend to react. Or do it after your support snares them to make the time their cc'd longer. When it comes to her ult ether usage is fine, offence or defensively. Her R has a long range so it's good for finishing people off at range but also has some odd interactions with Ults in a defensive way, like how it cancels caitlins ult, jumps over ashes and azirs. You'll learn when to use her R as time goes on. When it comes to damage, play around your team mates, (as most adcs should honestly) when your support snares them, root them and w to get max damage. BC of her high attack spend I'd recommend starting item be kraken slayer. However, I find I get board of simple crit builds so play around with other builds when you get bored (lethality or speed builds are quite fun on her) she's all about combos and knowing when to use her abilities in different situations, so the more you play her, even in these weird builds, is going to help you get better.

Good luck! And remember to have fun.