Rule number 1, never use your irons/straighteners on damp or wet hair 🙊. This will damage your hair, your hair should be completely dry before you begin using your irons to straighten your hair. If you apply heat protection spray before starting make sure you brush it through and give it a minute to sink in to your hair.
Sectioning your hair is the golden rule to getting the best result, work in small sections while the rest of your hair is clipped out the way. This makes life way easier.
Make sure your straighteners are given time to heat up to the right temperature that you need, don`t just plug them in and begin, give it a minute or 2 and then begin. So many people just start them up and get into straightening right away this will cause your hair not to be as straight at the sections you started on as the tool was not at the correct temperature.
You want to make sure you brush your hair through really well before straightening as any tugs will make your job harder, brush it through in sections, before brushing through your hair that is the perfect time to apply a heat protection product and evenly get it distributed in your hair by brushing. If your not so clued up on heat protection read my post here to help you out.
Always start from the nape of your neck and work your way up your hair, idealy the front should be straightened last. Section your hair into 2 sections, 2 at the bottom and 2 at the top, then you can work through and have the rest of the hair clipped out the way.
Invest in a pair of heat resistance gloves, these are perfect for handling straighteners and hot tools if you always find you burn yourself. Also a heat resistance mat is good too in order for you to safely put down your straighteners.
Clean your straighteners every now and then, residue of oil and dirt can build up on the plates so make sure you are wiping them clean every now and then.