Here are just some small rules for the artwork:
~Icons should be SQUARE. I find that 150x150 works best and gives a better resolution but of course, any size works as long as they are square.
~Banners MUST be 800x100 or a larger equivalent. Anything smaller will be pixelated and anything larger has the potential to cut off your work.

I will keep this forum open for about 7 days, so let me know if you need more time