How to deal with long hair?

I know this is for cutting hair/dying it but I have no idea where else I can ask for help. I have very long hair. It goes past my thighs and is a bit wavy. It's so long the curls just stretched out over time. Brushing it is quite a task and I have to wash my hair very often because it gets stuck in things, my scalp also gets very oily often which causes dandruff. I don't really want to cut it since it's the only thing that makes my appearance stand out, and I'm very proud of how long it's grown. I don't really know what exactly to do about it though. I'm not really skilled when it comes to haircare or hair styling. I'm currently using an Asian shampoo which has worked better than past brands. Any tips on how to style it/take care of it would be very helpful. I haven't had much luck when it comes to googling tips and tricks. I don't mind if there's any recommended ways for me to cut it even, I just don't really wanna cut a lot of it off.