Hair straigtening tips?

My mother says that I have to wash my hair directly before i straighten it..I normally wash my hair the night before and then in the morning I straighten it. Is she right? I want to buy a chi but she says it is no different then the 50 dollar one i bought at walmart could somebody tell me what is so great about the chi haow is it different from a conair one that was 50 dollars? An people that straighten their hair can you tell me your routine for straightening. Thx :)