wash your hair well, always use a conditioner - even on the ends if your roots are greasy.
use a cold rinse of water at the end of shower - tis supposed to flatten the cuticles on the hair so it reflects more light.
don't tip all your hair on top of your head in a turban, likewise don't scrub your wet hair with a towel - this will encourage knots and tangles.
comb carefully and slowly when wet with a wide-toothed comb, not a brush. spend money on a good comb that doesn't snag. if you have long hair get a paddle brush.
don't brush your hair roughly, or too much, avoid hairdryers and straighteners. avoid harsh colourants.
i sometimes use john frieda brilliant brunette and i find it absolutely fantastic, i buy it for special occasions. its a bit cheaper recently in tesco, and boots always have offers on shampoo. the rest of the time i mix it up with different brands but always condition my hair.
finally, for frizz, john frieda's frizz ease is amazing and has won many awards and topped serum sales. be careful though, only use a tiny amount.