Not knowing what sleep problems are involved in this question, a general idea about improving a five year old's sleep is to establish a regular sleep routine (bedtime and arousal).
You need to figure out why the child isn't sleeping. If s/he is afraid of monsters or nightmares you can get him/her a nightlight or spray "monster away spray" around their room. If the problems are not fear/nerves related I recommend asking a doctor just to be safe.