I think that the advice has been given in this thread by a couple of posters along with an excellent link.
Provide a proper temperature gradient, proper substrate, proper humidity, proper security and a properly sized enclosure. Make sure that any parasite load is dealt with and the animal will thrive.
As for diet, while we don't have access to african invertebrates per se, we can make do from insects available in order to replicate that diet as closely as possible. My savannah monitor was raised on smaller roaches and crickets. As he got larger, we moved up to larger roaches (we're lucky enough to live close enough to Mr. Tuttle of Blaberus.com and were able to get breeding colonies going for our ackies and the sav.
A healthy baby will eat and put on the appropriate amount of weight. The problem with most savs is that they are heavily parasitized and are often fed pinky and other crap from the pet stores or middle men that sell them. Once they are cleaned up, put in the proper environment and fed a proper diet, they don't need to bulked up.