In order to make it easier i usually deep condition before straightening. I then use a wooden brush similar to the spornette italian collection boar rounder while I blow dry. Make sure you divide your hair into about 6 sections and use the nozzle while you blow dry. I then use the organic Brazilian Keratin Therapy Ever Straight Flat Iron Spray while I flat iron.
Make sure you're using the right products. There are some great products out there that are designed to help protect the hair as well as make the hair stay straight. I got samples of the Motions 3-step Heat Styled System and use the Straight Finish Sealer on my daughter's hair when she wants it flat ironed. It does seem to protect it and doesn't ruin her curls when she wants to wear it curly. Hope that helps!