Sleep training??

Hey, ladies! What have been your experiences and techniques with sleep training? My son is 4 months old and his pediatrician recommended we start sleep training and said he really shouldn't need to eat overnight at his size. My son has never been a great sleeper. He was down to one overnight bottle, but recently he's been waking up to eat between 11-1 and again between 3-5. Regardless of when he last ate, around 4:30 every morning he starts waking up every 45 minutes to 1 hour. I feel like he's chronically under-rested, and I worry about how that might affect his development at some point. Long story short, I don't know where to start with weaning him from overnight feedings, sleep training, and improving the quality/quantity of his sleep. Help me!