Edit: I had the worst flash last night playing Maokai... I couldn't make up my mind whether or not to grab Nunu. :/
http://www.youtube.com/watch?v=385ZB7mZiBM
I was trying to figure out why you needed a fail flash to begin with. I mean, he was right there anyway!
I take it games didn't go well after I went to sleep last night
hey scy teach me how to elise
I run Spell Pen Reds, Armor Yellows, Scaling MR Blues, and Spell Pen Quints. Masteries are a fairly typical 9/21/0 page. Skill order is QEQW, R>Q>W>E.
Item build is: Boots3 -> Haunting Guise + Sorc Shoes (whichever order you can afford) -> Frozen Heart | Rylai's | Abyssal (typically only get two, almost always FH + Rylai's in some order) -> GA.
Laning is to just "if you can Q them, Q them" basically, though you can play it safe until Level 3 if you want. Don't bother harassing with Human W at low levels honestly. Rank 1 is 75 Damage for 60 Mana so it's not cost effective to spam it compared to her Q (95+8% CurrentHP Damage/60 Mana by the time you have Rank 1 W). Just rely on her Q unless you're all-in on them or you have W Rank 2 (125 Damage/70 Mana) or 3 (175 Damage/80 Mana). Your goal in lane is to basically force them to use potions early and to make them cautious about going to cs due to how fast you can drop them to half health. Jungler showing up to scare them (if not outright ganking them) helps make them extra wary about being at half health as well.
Once they're below half, you can then try to do one of her all-in combos:
Starting Human: Land E, run towards them, W, Q before Spiderling hits, switch to Spider, Q in, W. When they flash out, Rappel after them, Q, switch to Human for another Q if needed.
Starting Spider: Basically, the same as above but without the stun opening. You'll use that at the end after you Rappel in.
Edit: Alternatively, starting Spider: Bait them to engage you, Q them, W and stick to them. When your Q has ~2 second cooldown left, Rappel up. They'll Flash out (quickly E them before they get out of range) or they'll stay. Wait out the Rappel and land for another Q and then switch to Human for a quick EQW+Ignite. Generally, this is how I deal with Jax or Jayce. I get them to want to trade with me and then I Rappel out of the Jax dodge or Jayce W and just beat them in a straight up trade by avoiding some of their damage.
I tend to do the Human one when stuck in the middle of lane or closer to their turret and the Spider one when under my turret, though it basically comes down to whether or not I feel confident that I can land my stun. Don't forget your safest spot to harass is beyond the minion wave. This way you can kite further away from the wave and then Rappel backwards for an easy escape; if you're behind your minion wave, you basically can only use Rappel for the two seconds of invulnerability and hope they move somewhere you can drop to. Also, Rappel has a 2 second duration so abuse that if you need to wait for a cooldown to score a kill when low on health.
Team fight stuff is I just Human form harass them as much as possible. Try to land a stun on someone in the front that we can engage on (e.g., their AP carry, someone who's low from all the poke damage) and then Rappel beyond their front line and onto their ADC. Typically just stay in spider form for this unless I need to kill someone immediately and my Spider Q is on cooldown (/they're kiting me). You're just squishier in Human form so not much reason to be in it unless you NEED human Human spells (e.g., stunning the ADC, need Human QW for an instant 500 damage burst).