Hello XXXXXXX
To start with, I would like to mention that your history is not sufficient to make good possibilities as well as to give complete guidance. Yet on the basis of information provided I would like to tell few things and also ask you to observe and improve on some others.
First, you need to observe that do your friend have problem of sleep only or any other issues physically or psychological. Is he dealing with some emotional problems? Most of psychiatric disorder have sleep problem associated with them. If that is the case then you have to see a psychiatrist and get a complete evaluation for the problem and due treatment for that.
Second, has there been any recent change in life or change of residence. In such situations also there are cases of transient sleep disturbance and patient just need to practice sleep hygiene and if not getting improved than a short period of drug therapy and nothing else
Third, you have to see, that your friend have this problem for long time or developed recently, because most of chronic cases of sleep disturbance have either some medical illness causing disturbance in sleep or some psychiatric disorder preventing spontaneous resolution of sleep disturbance.
Fourth, Is there any history of substance abuse because who drink alcohol has changed sleep structure? Alcohol cause rapid sleep induction (means fast onset) but cause early awakening and thus sleep disturbance. Similarly smoking heavy during late evening hour cause sleep disturbance as tobacco is a stimulant and delays the onset of sleep.
Finally, if your friend has no such complains and just suffering from insomnia, than he has to follow some simple steps of sleep hygiene as mentioned below

No day time napping, how so ever tired he gets
Fixed time of going to bed and also for getting up, even if he had only 2-4 hr of sleep
No tea, coffee, cola and heavy diet in night
Bed should be used only in the night time. Not even for a minute before sleeping person should go to bed.
Take bath in warm water before going to bed, an hour or so before sleeping
No TV viewing when not able to sleep. No horror or mysterious shows before going to sleep. If anything to be used than it should be light soothing music in dim light and some light books to read.
If all this been followed religiously than majority of people with sleep problems respond.
Even after following this for weeks there appear no response than your friend need to visit a psychiatrist personally and get complete evaluation done and there he may be prescribed some medication for the same
I hope this advice may help you
You are always welcome to ask any more questions
Thanks

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