Most people would like to argue and say that Elise is only good as an Ability Power champion, however, I believe that she can be great as an AD CARRY! Elise has great range in human form, and great attack speed in spider form (with her W). I consider Elise to be a very, very versatile and fun champion. That being said, let's get on with the guide!

For runes, I recommend all Attack Damage Marks, all Attack Speed Glyphs and Seals, and all Attack Damage Quintessences. Why do I chose these runes over glyphs and seals like Armor and Mag. Res.? Elise has very poor base attack speed, and trust me, playing her as an AD Carry, you will want as much attack speed as you can get. Elise is also one of the best tower pushers in the game, with her spider form and W, with building attack speed, you can have turret gone in no time!

For masteries I recommend a standard AD Carry 21/9 page, with a bit of sustainability, just to keep her going early game. (You still have to be very careful and play very smart early game, because she can be VERY squishy.)

For items, I recommend starting off with Boots of Speed and 3 health potions.
On your first trip back to the base, you should have enough gold to buy Berserker's Greaves, Ruby Crystal, Long Sword, and maybe a ward or two.
If you couldn't tell, you're going to start build a Phage, so on your next trip back, finish your Phage, and buy a Zeal.
The rest of the item purchasing is completely up to you. If you are against a heavy damage team, you might want to go ahead and buying the sustain items (such as Frozen Mallet), or if you're doing great without the extra health, go ahead and start building your Phantom Dancer and Infinity Edge.
In the end, you should end up with a build similar to this: Berserker's Greaves, Frozen Mallet, Phantom Dancer, Infinity Edge, Bloodthirster, and Madred's Bloodrazor.

You're going to want to start with your W, being that you aren't building any Ability Power, and Volatile Spiderling has the highest base damage out of all of her spells, plus, when in Spider Form, W is your main source of damage. Go ahead and get Q, then E. Then, start maxing in this order: W, Q, E.

I prefer to use Flash and Ignite for my summoner spells, Flash is a great tool for escaping, or chasing. And ignite is great if you just couldn't get that last hit!