There are the days when sleep isn't just possible. Either you know you're supremely stressed or you're not very tired due to a disruption in your sleep cycle, or you're overtired and left wired. I have a few tricks up my sleeve that help me, and will hopefully help you!
The biggest rule of thumb I think is to tire yourself out. Do as much as you can in a day to be productive and also help your sleep cycle. If that isn't enough, then make sure you add in a workout. Working out can release stress, toxins, and will help you sleep better at night. Also try a yoga routine when you wake up or right before bed. I find yoga to be a great help.
Have a sleep routine in place. By this I mean to go to sleep at almost the same time per day and wake up at roughly the same time. If you keep this in check it should keep your inner clock in check too.
Set time before bed to relax. This is key. Either you can read, watch TV, lie down, anything that lets you relax. Then before bed, unplug yourself from the world.
Try a bath or aromatherapy. There are plenty of bath salts and body lotions that can help with sleep. Look for products with lavender in them as lavender is a good sleep aid. Some of my favourites are from Bath and Body Works and Johnson & Johnson's Baby Bedtime Lotion.
My pup, Bingley, is a great sleeper. Hopefully this will help in getting a better sleep. If not, try counting some sheep. Happy sleeping!