Most Helpful Girl
This is from personal experience, it's actually worked for me and my hair quality has gotten so much better. I used to have really bad, chemically damaged hair, and now I can actually let it dry naturally and it doesn't look half bad.
The main idea is to improve your hair internally by what you put into your body; that being said, taking certain vitamins can drastically improve the quality. What I used to do everyday is make a sort of milkshake that's made out of flax seed, soy milk (I just prefer soy milk since it's better for your skin), some fruit (usually strawberries, just a preference though), and one organic egg. It might sound incredibly gross, but /trust me/ on this. Eggs contain protein and several other vitamins beneficial for hair. Also, don't worry about it being unsafe or unsanitary; I've read several articles and my dad's a doctor, and I've been assured that it's completely alright. Plus, once it's blended in, you can't even taste it.
With my shake I also take a crap load of vitamins that are good for hair. There's certainly more out there, but I usually just take:
along with some random Polish vitamins that are specifically good for hair, I have no idea what's in them but my grandma brought them over ahaha. Anyway, yeah. Doing all of this will improve your hair's quality by making it stronger and thicker/fuller. I get way less breakage and the frizz has disappeared too. Doing weekly deep conditioning is good too; you can either buy a deep conditioner, or you can just use olive oil. Using keratin also helps, but if your hair isn't too badly damaged, you might not want to do this too often, especially since you're already taking in protein with the shake/egg.
There's many more tips and tricks out there for healthy hair, but this is the main one which has really changed my hair for the better. It also just makes me feel better in general. I swear this is the equivalent of liquid gold.