Lots of water before going to bed (or ideally, combined with the alcohol intake, 2 glasses of water for every glass of alcoholic drink) is the best preventive measure I know. I guess drinking afterwards might also help.
I don't know how well they work (if at all) but there's quite a market for 'hangover cure' drinks in Japan[0], and I've heard of a tradition of drinking citrusy supplements or anything high in Vitamin C in Japan. It always sounded off to me, but I suppose it would help with mineral depletion.
I'm a believer. I don't care if it's superstition, I'll take a gram of C at the drop of a hat. I love the Japanese hangover drinks, E-Mergen-C is not quite as tasty but 30 of them take up the volume of 3 bottled C drinks, for the small kind.
Works better before, but will improve disposition the morning of as well.
Can confirm that. If you're drunk, drink as much water as you can, expel it and drink again; this will help a lot to soften and shorten the hangover, effectively reducing the amount of alcohol in the blood.
This is the method that works for me. If I go heavy on water between alcoholic drinks I can avoid having a hangover entirely, or at least reduce it to a very mild headache that Ibuprofen can deal with.
The only downside is you will have to use the bathroom a lot.
[0] https://jobsinjapan.com/working-in-japan/japans-famous-anti-...