The equipment you use is also a big factor, I straighten my hair daily as I plait it every night and as a hairdresser know the damage that can be caused however i can't walk around scruffy lol i use professional products throughout and treat my hair every 4-6 weeks as its extensions it's easily damaged but its fine, my straighteners are fast so you don't need to keep going over and over just run down once and done so no cheap 20 pound jobbies xx if your straighteners snag you hair scrap them, they'll do more damage than good x
Invest in professional shampoo and conditioner and heat defence to keep your hair in best condition. I recommend joico x