always always try to drink as much water as possible before going to bed. Just ram in as much as you can without being sick.
Also, if you are sick at any point then you must drink a lot of water afterwards, as you will be even more dehydrated as you have lost all the water from your stomach.
If you wake up still drunk or not hungover, but know you ought to be then take this as a blessing and get as much water in as possible.
As a general guide, drink as much water as you have drunk beer to be sure of no hangover, dont mix either, as mixing is what really gets you. it is possible to drink 12 pints of beer and then drink a load of water before bed and avoid a hangover (although u will be bloody shaky and driving is not a good idea in the morning i found out), but if you drink, say, 5 pints, 2 pints pimms, 3 glasses wine and some gin (which of course i would never advise as this would be obscene and ruins the pleasure of drinking blah blah blah
) and then drink a whole load of water before bed, you will still have a screaming headache at 5 am
Food wise, always have a nice large meal for lunch before drinking and have a nice big meal while your drinking if the time is appropriate, this will mean your blood is full of sugar and will keep your brain happier, if not better hydrated.
One mistake that can be made in an epic drinking session (an all afternoon to closing time one for example) is to miss out tea cos your too busy/drunk, cos this will not help
So basically the golden rule: water before bed. water after you wake up. and food.
Once you are hungover, i find eating lots of food (sandwiches always good and potato based stuff as the stomach can absorb them easily) and lots of water or orange juice are good.
If you have a dodgy stomach and a headache DO NOT TAKE PARACETEMOL!!! this will make your stomach 10 times worse even if it does get rid of your headache.
As you can tell, my gap year has not been wasted