Hot milk with some form of alcohol in it - generally whisky or rum or brandy (literally about a thimble-full and no more).
A hot bath with lavender...
Kalms or Rescue Remedy..
Make sure your bed, pillows and matress are comfy and clean.
Have the room as you need it to be - have it silent and pitch black if need be, or with a light and the radio if that helps..
Don't have the laptop, TV etc in your room if you can help it.
Wind down from about 3 hours before going to sleep, go for a bath, read, listen to music, go for a brisk walk, have a hot drink.
Big one - don't think too much about sleeping, don't worry about it, as it makes it worse!
Oh and don't take Citalopram unless you were prescribed. I'm on ecitalopram and that makes me drowsy as hell but they might have the opposite effect entirely on you.