I would pull tail rather than plaiting it. Is more fashionable than plaiting. As one of my yard friends said (who has been showing for years and done well!) "plaiting is very 80's!! Until I started showing last year and constantly picker her brains I had no idea there were fashions, but there are! You can use a razor comb (like I do) if pulling bothers you or your horse.
Do it gradually as well. I always start pulling a few weeks before a show then just keep on top of it. I have been known to get a bit carried away with a mane and at least this way it can grow a bit if you do.
I have a snuggy hood turnout hood. I plait the night before and then put this on. Is a lycra hood with a silky bit for the mane so its hard for them to rub it and pull plaits out. My advice is make sure it fits! This is my second one as the first one I bought was a cheap lycra one (not snuggy hoods) and he got it over his head and roound his neck and distroyed his plaits, so waste of time!
I dont wet the mane or use gell as its too wet to work with, but this is the norm. Dont use main or tail spray less than a day before you plait. It does make it lovely and silky and easy to comb, but too slippery for plaitng the mane. Use it after plaiting if you want.
Some people section off (odd nos) first then plait. I know some poeple who section and plait as they go. This is up to you really. I find sectioning first helps me make sure the sections are equal sizes. Nothing worse than one or two big fat ones and lots of thin ones!!!
If you are showing then thread is best and will hold them in tight. I always use thread if plaiting the night before a show. If Im off to local dressage I cheat and use bands and plaiting tape as its quicker, but tend to do it in the morning as I enter the later dressage classes.
Leave an hour for mane plaiting as there is nothing worse than rushing. I take about 1/2 hour now for good plaits but this took some time. Im sure many more people can do it quicker, but Im getting there! Plaiting with thread does take longer than bands.
Have your horse either eating his feed or standing settled. Mine will normally fall asleep! but if I give him a hay net the action of him pulling out the hay jerks his head about and annoys me!
Hope this helps. Sorry for the essay!!