Do you straighten your hair and it turns out to be really straight?If you do,please answer!?

I am kind of annoyed with my hair straightener or myself because my hair can never stay perfectly straight after about a half an hour of straightening it.I have "Conair Infinity" it is AMAZING,but it doesn't stay straight.Like at the ends,it turns a bit wavy during the day.I can't afford to buy CHI or any really expensive ones right now,but I would like to know step by step how you do it.10 points best answer! Thanks I appreciate it!