I agree that routine is key. Dinner, bath and bedtime at the same time every night. Maybe do a lotion massage after the bath to completely relax your baby. If your baby cries when you place them in the crib, Go in every five minutes to console them for a minute or two and place them back in their crib. Keep repeating this. I promise it does work eventually. It may take an hour the first night but they will soon become accustomed to bed in their crib and it becomes a lot easier usually after five days of doing this. The crying maybe hard to deal with while you do this but just remember crying doesn't hurt them and it makes their lungs stronger. :) you can do it!
Is baby waking up to eat or to play? Feed him plenty during day till bedtime, make sure he's playing a lot to tire him out in the day, but limit naps after 2-3 pm to just a short rest then do calm things in evening after dinner no rousting him up with giggles and fun but just calm play puzzle books talking music etc. routine works best.
what helped with mine was...darken the room every time its sleeping time. If they wake up in the night I feed them quiet and put them right back to sleep. No playing or talking (not talking about newborns) Have a stern night time and get up the same time every day.