Exercise during the day. Don't nap. Wake up earlier, go to bed a tad bit later. Don't eat anything after 7pm. Stay hydrated.
If you're still having problems, just close your eyes, and think about nothing other than sleep.
Insomnia is common at this point in pregnancy as your body is preparing you for what's to come. However, you need your rest to stay healthy, and to keep baking a healthy baby. Trust me, you'll want all the rest you can get before baby arrives.
I'm 36 weeks, due 2/8, and if I'm not active enough during the day, you may as well forget that I own a bed and know what sleep is.
Try to relax before going to bed and use lots of pillows like under your bump and between your legs. I had insomnia few weeks ago because I was thinking too much about everything. Maybe try to work out if there's anything bothering you. I was worried about finances and not getting all the baby stuff on time but once I got few bits and spoke with my partner insomnia left me alone.