I'm still in my building a regimen phase but before (and I do plan to go back to it if these "rules" do nothing for my hair) these are the practices I learned NOT to do but did until recently.
Detangling before washing (I didn't use to saturate my hair in conditioner, I just combed it out dry!)
Not using heat to deep condition (a lot of times I'd keep the conditioner in for a few minutes before rinsing it out)
Not using a leave in conditioner (hey, didn't know what it was until recently )
Using grease a styling aid (yes I would grease my scalp and it did set my hair well, just used a bit too much at times)
Always, always forgetting to moisturize and seal. (didn't learn about it until recently)
My hair didn't suffer from it, it just suffered from the perm I got when I was 16, and when I was younger I never even conditioned. My hair stayed in braids so breakage wasn't really a problem just need to retain length.
I may go back to my old practices though (but will incorporate some of the new practices like conditioning, etc. if it'll help me retain length.