I've found that focusing on my breath really helps. There are some great apps with guided breathing exercises for sleep, and I find the calmness of it all very soothing - almost meditative.
Also, instead of trying to force my mind to shut down , I started visualising all those racing thoughts as actual objects flying around the room. Somehow, putting some physical distance between me and my thoughts helps shrink them down in size so they're not so overwhelming.
Hope you find these tips helpful. Would love to hear others' suggestions too!