I feed on a schedule that looks something like this:

up to 350g rat pup every 5 days

350-700 weaned/small rat every 6 days

700+ med every 7 days

Typically you should feed a prey item whose weight 10-15% of the snakes weight. I tend to feed a prey item that is 15% and I stick to the schedule. If they dont feed then I will try again on the next scheduled feeding day.