please help

My son is 9 months. Hey falls asleep on his own for his naps, I don't know why at night when I put him to sleep he never seems to fall asleep on his own. When I put him in his crib he would cry and then eventually fall asleep and then wake up again and cry then sleep. What am I doing wrong? We have a bedtime routine and he's usually awake for 4 hours before I put him to bed.