Congrats on your new ball python!
A general rule of thumb is to feed your snake once a week with a mouse/rodent sized the same as the largest part of your snake's belly. Also, you have to supervise your snake eating at all times when feeding live!
Here is a link on how to post pictures to this forum.
http://ball-pythons.net/forums/showt...-Post-Pictures
Edit:
Just noticed that Eric posted this link just before me
To clarify on his post, you should put a coin (That we can tell the type of) next to your ball python in such a way so that it is easy to see the diameter of his/her largest spot.