A good and effective solution is to let your baby cry, but not for too long. Try putting them to down and then setting a time limit. Make it short at first, say three minutes. If your baby is still crying after that time, go in the room and soothe them and let them know you are there, but don’t pick them up. After that time, extend the time to five minutes before you go in, again, don’t pick them up. Keep extending the time it takes before you go in and check. Your baby will learn that you are there, but that you don’t come right away when they cry. They will eventually go to sleep; you just have to stick with it.
Be sure to implement a consistent bed time routine that you use every night. This will help as well.