Thought Lulu was just a support did you? Well, allow me to inform your that given the right team composition, she can be the most broken ADC-its nearly impossible to lose lane with her if played right. Do to the slows and poly morph, she is nigh impossible to dual against. The one down side is that her strength fall off late game as she can not scale as well as traditional carries; shes makes up for this however with her early and mid game dominance.

I prefer to just use standard ADC runes: Armor Penetration, Flat Armor, Scaling Magic Resist, and Attack Damage. If you are feeling more confident, you may want to swap the MR glyphs for scaling attack damage ones to better your late game (which is where Lulu starts to fall of).

Again, very standard setup for the masteries, no need to explain, as with all ADCs 21/9/0.

Ah, here's where it gets fun. I prefer to start with a long sword and health pots, a fairly standard start, however, I would dissuade you from buying boots to start as Lulu can cast Whimsy if needed and should have any trouble controlling lane positioning early game with her Glitterlance. As for last hitting, obviously the extra early damage helps, but it is very easy to do so regardless as Pix does most of the work.

Pros:

Very strong early game
Her slows can contribute a lot to team fights
High dueling potential
Can last hit all the creeps with Pix
"About to kill me? Oh well I have an ability that gives me 600hp with a 60sec CD"

Cons:

Falls of late game in terms of damage
If you don't have a good support, it will be rough
Requires a high damage jungle or top laner for late game
Can be shut down by high jungle presence (shes strongest early game so she can be shutdown)

This is important! Lulu is only a viable ADC given the correct team composition. You very much need an aggressive support i.e. Blitz, Thresh, Alistar. Also your top or jungle needs to be a high physical damage champion else late game your team may have troubles. A jungler with knock ups or hard CCs is also ideal, as this will make it very easy to bully your opponents completely out of lane. Lulu is amazing in team fights with her ult and CC abilites; making her a valuable asset to disrupting and controlling team fights.
An example or an ideal team comp. including Lulu would be one such as: Top Tryndamere/Jayce/Vayne : Jungle Malaphite/Nocturne/Trundle/Ammumu : Support: Blitz/Thresh/Alistar.