Been a long time since I've tried it. Q is still your best option for leveling; Spider W is unreliable at melee since bot is the CC lane atm and E adds no damage and only adds stun 1.5 sec > 2 sec. Be sure to use targeted void spiderling: W - R - Q. Careful not to hit minions with it, as ADCs will be on edge from an Elise Support in the first place.
In 2v3 situations that are going sour, run in the other direction than the carry if caught too far, even if toward enemy base. Then if they somehow decide to let the carry go to chase you, you can Rappel on an enemy to attempt your escape. At very least, you usually give your carry a chance.
If an enemy is low at tower, she's the easiest to dive with. Go in at close range and try for a point blank Cocoon. If that hits, you're still not focused by tower because it does no damage. Proceed to combo the enemy, and if they are about to take you down somehow, usually you can Rappel right out of danger while your carry finishes them off, if they even survive that long. Either way, things rarely turn sour, save a timely gank. Even those can turn your direction in certain situations.
I'd suggest Coin/Spellthief start. Coin plays toward your ready-to-pounce-assassin tendencies, whereas Spellthief is strong at whittling down enemies with your ranged damage. She doesn't really pull of shield with low base ranged AD and lack of melee tankiness.
Overall, though, I'd be wary of trying it. Most supports are going to have strong late games, whereas Elise will compound any problems you have early game, which are likely with her unreliable CC. She might do okay in a kill-thirsty comp, but a couple beefy tanks can crush your dreams quite easily.