Hmmm... my usual initial advice would be to take a long, luxuriating, girlie pampering soak in the tub, taking advantage of the fact that the kids are in bed... but I guess that's not possible at the moment - d'oh!
That's usually a help... then as your body slowly cools from the heat of the bath, it's a great way to relax into much needed sleep...
Otherwise, try relaxation techniques... play some soft music in the background... I can't tell you what sort of music helps me cos then I'd out myself as a complete hippy & I'm supposed to be being a rufty tufty biker bird type
Ah sodditt... OK then... check out an outfit called "Bliss" - try A Hundred Thousand Angels for starters... it's just gorgeous and SOoooo relaxing. (Disclaimer: I'm not a hippy! This isn't even my nose! *ahem*)
Lie quietly and still... on your back, everything relaxed... arms by your side, palms down... once you think everything's relaxed, start *really* relaxing... start from your toes/feet and work up to your body, then your fingers/hands... you really will feel the difference once you start thinking about really relaxing all your muscles... take slow, deep breaths (2 in, 4 out works for me - some prefer 3 in, 3 out) and with each exhalation think "relax". You'll actually "feel" your hands sinking down into your mattress and when you get as far up as your shoulders/neck, it feels like a massive weight's been lifted
Doing it this way is FAR easier than telling yourself to empty your mind... the minute you start thinking "Right, I've got to empty my mind of all thought" it goes into overdrive and every little niggle of the day sets in at once... giving your mind stuff to do will automatically clear it
All this from the woman who managed to sleep from 3am to 6am - woohoo! Check me out!
It doesn't always work - I can't promise results, but it's well worth a try. After all, I'm an expert in insomnia