Dear reader, this is my first guide on the newest Champion Elise. I hope to make a guide you will enjoy using ^^.
Most guides as well as the recommended items ingame sugest u play Elise AP. I disagree on the matter. Except for the w her ap ratio's are not sufficient to play her that way. Also if you gonna look at her abilities they fit better an AD user then an AP user. In humanoid form she has 2 ap moves and a stun, in spider form she has "3" ad spells (a strong attack, attackspeed up and a gab closer).
Hence if you play her AP, you will lose half of her strength same goes if you play her AD. I think Hybrid is the way to go with Elise.

Greater Mark of Precision well to do maximum damage through the game

Greater Seal of Defense for extra sustain

Greater Glyph of Scaling Ability Power to gain ability power.

Greater Quintessence of Attack Damage for early damage and easier farming.

Core Items:
Trinity Force vs Lich Bane
Both can be used, since this build the damage outcome wont be that much different.
I prefer Trinity force for extra attackspeed, more movement and the passive to slow 25% chance.

Hextech Gunblade for both damages and lifesteal/spellvamp

Nashor's Tooth is made for her ^^

Recommended:
Guinsoo's Rageblade gives a nice effect with w in spider form.

Boots of Swiftness to get from A - B fast but also to chase down your enemy. With this build you will be able to catch up to most champions.

Mercury's Treads are also good for chasing since its tenacy, also better for sustain.

I first max my q wich helps in farming and dealing a lot damage against opponents. In humanoid form is this my favorite skill to use.

I max W after that, in spiderform this is my sweet thing it ups your attack speed on lv 5 by 120% :O ideal for burst damage. In humanoid form it launches a spider wich is hard to land since it walks to the closest target and not neccesairy the opponent you had in mind.

Last the E, both in Spider and in Humanoid form the skill itself does no damage, u want it to stun your enemies or to ambush them. Upgrading this skill only reduces cooldown hence upping this skill early or mid game is rather fruitless.

In order with my masteries I prefer Ignite and to get away Flash.

Other spells you might wanna try are: Exhaust and Heal.
Elise has only one CC to stun and targets are gonna run pretty fast, in early game its pretty hard to kill with Elise.

Heal, except for the standard use it also heals ur spiderlings

In order to chase down or get away you can use Ghost instead of Flash.

Surge can be used depends on your priorities.

Normally you wont find yourself in mana problems so i wont use Clarity.

I wont use Promote, u got your own lovely spiderlings to do the work.

+
Has Sustain
CC
Gabcloser
Allround you can always find a place on the map (jungel/top/mid)
increased stats in spider form

-
Hard to farm with
Hard to kill early game
Not enough sustain to tank