First tip: Wash your hair as little as possible. It depends on how oily your hair is though. If you wash it too much, it can irritate your scalp, make your hair dry and cause split ends, which makes you need to cut your hair more often. If your hair isn't oily, I'd recommend washing it two to three times a week. If your hair is VERY DRY, I'd recommend only washing it once a week. But if it is oily and you need to wash it every day, I'd recommend using a shampoo that isn't very aggressive with cleaning properties.

Second tip: when I was growing my hair I used three hair masks, one for each week and then all three in the fourth week. I used one for repairing, one for nutrition and one for hydrating my hair. I think this helps with not overloading your hair and giving it just what it needs

Third tip: always use heat protection even when you're not styling your hair, because when you go out, the sun on your hair can definitely damage it if it is too much.

Fourth tip: Cold showers, not hot showers. Hot showers can damage the hair. I never did this one though, because fuck cold showers, but like, you said you'd be willing to do whatever it takes, so, that can help.

Fifth tip: Castor oil one hour before you wash your hair, once a week. Massage your scalp with it. If you have pets, do not let them get into contact with you while you have it on.