I go r > e > w > q in skill building
Start ring and potion
I'll start with either q or w, depending on my opponent. If I can easily harass, q, if I can't get near, w is better. Learn to judge where they'll run into after the delay on w. Get some weak harassment in with q or w to take them down a bit. Get all three skills by level 3. From there on, if you can land your snare, run in with e and q dropping ignite as soon as e is on them. If you're doing it right, you should have a kill between levels 3 and 6.
Back to base? Start working on that Rylai's scepter. Finish it, get rod of ages. You're tanky and AP isn't your concern by late game. I like to get Frozen Heart. Spirit Visage is great for your ult, and I like Force of Nature for most of my MR. Game should be done by now. If not, try Hourglass.
In the laning phase, you're a beast. If you are getting out harassed, play it cool until level 6 where you should destroy them. Mid game you should be ganking lanes fairly easily. Late game, you're off tank/utility. Someone's trying to run? Snare. Carry being attacked, snare/slow. You'll be in the middle of all fights, most likely. So pay attention and do what's best for the team. You probably won't be killing much by the end, but that's what your actual carries are for, ^_^