For children who are old enough to understand is can be a good idea to role-play how to go to sleep with your infant.  Simply go to your infants bedroom during the day and with a doll or teddy-bear role-play going to bed.  Get your child to put the doll into bed and read it a story and sing a song or whatever your going to bed routine is.  Then tell the doll that you are leaving the room but will be back to check on them in 2 minutes.  After 2 minutes send your child into the room to give the doll a kiss and tuck it in.  Do this again after 5 minutes and so on until your infants agrees the doll is asleep.  Then at night time do exactly the same thing with your child!  This is a crucial part of teaching a child to fall sleep by themselves.