When is a good time to start doing sleep training?

Early. What we think of as true sleep training, the "cry-it-out" variety, probably is not appropriate until 5 months or so. However, start helping your baby learn how to sleep early on. By 2 months, if baby's weight is good, give him an opportunity to go back to sleep at night without feeding him. Develop a consistent bedtime routine that separates sleep from feeding and helps him learn to self soothe.
Sleep. It is important to start a routine as as early as possible, by six to eight weeks of age. Your baby can see color and detail, also hold his/her head up, and will recognize your voice and be sooth by it. Once you notice these changes, it’s time to introduce healthy sleep routine.