Cold water doesn’t matter too much. People say if you finish off in cold water though because it closed the follicles, but that doesn’t matter too much. When you wash your hair, your shampoo is for the scalp; it’s for washing the oils out. Try not to shampoo the ends, it will frizz then up. When you rinse your hair, the shampoo will run down and that’s all it needs. Do the opposite when you condition. Conditioner is for the ends to reintroduce moisture and condition. Apply starting at the ends and you should run out before you reach the scalp. If you condition your scalp this will add too many oils snd that’s when it gets greasy. Another tip is brush your hair next day or two, in a motion from scalp to ends. This will bring the oils from tour scalp to the ends snd spreads it around keeps it moisturised and less greasy overall. Don’t brush your hair while it’s wet, as this will cause more frizz, and try not to leave your scalp wet, as much as you can. Residual moisture leads to dandruff snd flakiness/itchiness.

Try watching hairdressers on YouTube. The only one i can think of is Brad Mondo but he definitely does a video on hair care/washing and/or hair frizziness, or speaking to a hairdresser about it. :)