Try this simple breathing technique:
Focus on your breathing, relax your body. Gently inhale through your nose for a six count, gently hold for a 3 count, and then exhale for a six count. Do this 4 times.
Then do the same, but without the 3 count pause. In for 6, out for 6. Nice slow, gentle breaths.
In 8 breaths, you will have a nice balance of O2 in your blood, and focusing on the breathing will help your mind focus on something.
Everyone has slightly different lung capacity, depending on anatomy and if/how long you ever smoked... so if this is difficult, shorten the cycle, if you find that you aren't getting enough of a breath, then simply increase the duration. Just make sure you balance your inhale and exhale.
Also, I am sure you know, but I will reinforce that nicotine is a stimulant. If you must
vape around the time you SHOULD be going to sleep, get yourself a nice 0mg
juice in a mellow flavor.. say, earl grey tea, or honey vanilla.
Another trick that worked for me as a kid, and worked for my son as a kid... a mug of warm milk with honey... between the warm milk, the lack of stimulants and breathing technique, you should be off to dreamland in no time flat.
Or not. F&*#@ing insomnia has me too! It's 12:30 and I'm still posting tips on how to go to sleep.. who am I kidding???