As this is my 1st real guide on this Champion it may be a little lax on full explanations. However i am hoping it will be helpful for somebody who has never used her. Also who knows maybe it will help Riot by getting somebody to buy her for RP. It doesn't matter to me how she's purchased however, i hope you all will like her as i have.

This build will cover the basics how how to use her, as any other Champion they can be played differently to how YOU are comfortable. The examples and ideas are how she works best with me. If they do not work for you please feel free to change them up a bit.

1/30/13 Added items for certain situation and other details.

Magic Pen to avoid buying anything that will need that and focus more on AP/AS.
AS ruins for your passive to kick in more often at lvl 18 with the full build you will be hitting with your passive ever 1.7 seconds or so for an extra 700 cleaving damage. Late game it would rape a 5k hp tank in no time.
Scaling AP why not? I couldn't think of anything more useful to put there. If you have ideas please don't be shy and share them.

The offensive part should explain itself, the defensive part is just to be a little less squishy at the start. As you may be mid, jungle or top. I would suggest it in the event that you will be moved to another lane in the middle of a game.

Pros
Super Powerful
Can take our squishy champs easy
Will do well in team fights
Can engage quickly
Can target the opposing teams main treats 1st with her R skill.

Cons
Will often be targeted 1st so change your tactics when running in.
Low HP, even with the shield a good burst set will kill you.
Is made more to engage than to run away

Practice you Q strike, either from far or close. Lead with the skill, don't aim where they are. Aim to where they will be. Only use your R to get away, if an enemy has Moonlight on them or if it's for the sure ace. Shield often when you're in the middle of a fight and don't forget to save your e for if they have a chance to run away.

She is one of the easiest to gank with because of her R skill. And she'll rape thought most champions with easy before they know what hit them and still make it out alive because of her shield. Once the 3 balls hit somebody with this build finished it's a 1000 point shield.

Last one in, work from the back to the front.
Flank your enemies often as you can Q through walls and often R shortly after. You should always be coming out of "nowhere" to gank the enemy squishies(because they can mess you up).