For a long time I didn't like having curly hair. It was ages before I realised that it was just that a lot of hairdressers don't know how to cut it. Obviously, there's more straight hair in the world than curly, and also curly hair acts completely different when it's wet (...it goes straight) so you kind of can't blame them, but still.
One of the basic principles seems to be "layers", basically letting the stuff on top be longer than the stuff underneath. (You can tell I'm not a hairdresser.) Before I went to anyone who knew this, either the top would look right, or the sides, but never both!
When I had my hair cut today, the hairdresser did a trick I've not seen before. She would take a little bundle of hair from on top and twist it into a tightish spiral, and then make a few nicks halfway-through the thickness of that spiral. So the end result is that that bundle of hair gets cut to different lengths, but apparently without going frizzy. I've no idea how the mechanics of that works, but I'll take her word for it.
The other thing that helps is "product". Some hairdressers have put gel on my hair and that looks absolutely rubbish, it basically sends me straight to the 80s. The place I go to at the moment uses stuff called "curl cream" (and the even more pretentiously-named "soufflé"). Who knows what they are? I can't tell you, I could tell you what's on their ingredients list but it's basically all the usual stuff you find on those bottles (copolymer this, cyclomethicone that, and of course "aqua"). It's not like gel because it doesn't hold as fast, but it seems to encourage a softer kind of hold which sort of lets curls curl together and not fall apart. "Curl cream" isn't a household phrase so I can't look it up or work it out...
Oh and something else. On the internet you will find various bits of debate about whether people with curly hair would benefit by not using shampoo - the reasoning being that shampoo gets rid of natural oils that let the hair curl non-frizzily, something like that. Some websites will tell you not to use shampoo at all, just use conditioner. Well in my experience that advice is along the right lines - but don't completely avoid shampoo, because your hair needs a proper clean now and again. For example, I wash my hair regularly but with nothing more than conditioner, and then maybe every two or three weeks I use shampoo. It doesn't look its best after the shampoo-wash you see, but it's certified clean :)