Its very unusual to play elise on mid lane, but its better than most people think. You almost one hit many enemys if you build full ap.

Pros:
-Noone plays it, so noone is prepared for it
-DAMAGE
-6 Abilities


Cons:
-No Real Ult
-Escape is only possible to enemy targets, otherwise you have to hang around until you fall into your enemys

Stay in human form to farm on the lane, use your Neurotoxin to poke and after your engage kombo, fight in spider form until Cocoon is ready again or until your enemy is dead.

And dont forget to ask your jungler for blue buff :D

Engage:
Cocoon -> Volatile Spiderling -> Neurotoxin -> Spider Form -> Venomous Bite -> Skittering Frenzy

Chase:
Spider Form -> Rappel onto enemy or enemy near him -> Venomous Bite -> Human Form -> Cocoon -> Neurotoxin -> Volatile Spiderling and if he isnt dead yet, ignite, repeat this or do Spider Form -> Venomous Bite -> Skittering Frenzy