Yeah you just describe what you want and they will tend to do it. I just get away with walk-ins at JCPenney salons, but if you get particular about your style you can find a stylist or barber that can learn how you like your hair.
My hair was about 3ft long at the beginning of last year. I’d normally go for a haircut every two to four months and ask for them to take two inches off and add layering.
Last summer it was getting too hot gardening with how thick my hair gets, so I asked for the back of my head to get shaved as an undercut about at my glasses line. Hair looked the same when worn down, but I could put it up to cool things down. I had to go in every month or two though to keep it short enough to keep me cool, so every other haircut I asked for two inches off and layering.
I let the undercut grow out from October to June, and had maybe 6 inches of hair? With no layering it looked a bit flat when I wore my hair down.
This summer I decided to get a Mohawk for better ventilation. Asked for the sides to be buzzed leaving about a 4 inch wide strip running from scalp to back of neck, for 6 inches off the longest part of the hair that was not originally part of the undercut, and layering to be added to both the longest portion and what was the undercut.
I typically wear my hair to the side, so it looks like I just have a little undercut and can pull my hair back when gardening to cool off. It would probably look silly if I put up my hair with gel, but after 6inches of hair it really is a pain to put that up. Also I have a kid, so there is no time for extensive styling.
Over winter I’ll probably aim for every two to four months for haircuts since I don’t need the sides so short. Goal is probably 6 inches off the longest part until it levels out, and then just decide how long I want it in that style.
Whatever feels good for you, but generally they tend to rest on your hole like a sleep mask. If you have enough movement to be chafing you might want to look at something with a bit more coverage.