I feed mine once a week, mouse weanlings for my smaller snakes and small to medium rats for the larger ones. A good rule of thumb is to feed prey items about as thick around at the hips as she is at the thickest part of her body. I will also point out that feeding a second prey item is to be done at your discretion. Just because a snake takes the second mouse/rat doesn't mean they were particularly hungry (as snakes are opportunistic feeders and will often eat even if they aren't very hungry), and just because they refuse one or both food items doesn't mean they're full or satisfied (ball pythons are notorious for fussy eating habits). Getting into a good feeding routine helps a lot, which for me means offering each of my snakes one properly sized rodent around the same time on the same day each week (and disposing of the rodent if it hasn't been eaten within an hour or two).