How did you get started? What size photos did you use? Are they all the same frames and size or did you mix it up?

I want to put a gallery wall behind this Ikea dresser that we are painting navy blue:
http://www.ikea.com/us/en/catalog/products/10221421/

I am not a crafty person. I am horrible at it actually but I really want to do this ! Any help and advice or cool tools you used I would greatly appreciate!