It depends on what you are using. First, I always pre-stretch my hair before using heat to straighten. I air dry in large twists, rollersets, or blow dry to stretch my hair. I then section my hair and detangle with a smaller tooth comb completelty from root to tip. I then use the flat iron to chase the comb all the way to the ends. I can usually get the hair straight with on pass using this technique. When I use my ceramic electric hot comb, I make sure that the back of the comb is used to smooth and straighten the hair. Because my hair has been stretched to a blown out state before I add heat, I do not need high heat to pres out my hair. Actually, as my rollersets improve, I can get my hair pretty straight rollersetting under a soft bonnet.