I have pretty curly hair. It's not as curly as it was when I was little. It's really thick and full of volume. I used to have really long hair and personally that was easier to straighten for me. I got it cut to my collar bone and it has grown out since then. I have learned how to straighten it faster and make it smoother. With longer hair it is better to have a two inch flat iron ceramic based coated straightener. I found that Conair had the best one for longer thick hair. Now I have a one inch Revlon Stylix. It heats quickly and doesn't fry you hair.
Get started by washing your hair. Shampoo rinse then squeeze out any excess water that you might have dripping and then apply a good amount of conditioner that gets to all of your hair without having too much. Let the conditioner sit on your head for about two or three minutes so that the nutrients and oils can soak into your hair and scalp. In the mean time you can wash your body or do whatever while you're waiting on your hair. After the two or three minutes rinse out your hair completely with cool water. It is good for your hair so that it doesn't get split ends as fast and it will help make your hair shinier in the future. When you are done in the shower towel dry your hair enough that it isn't dripping anymore. If you have time I would suggest that you just let your hair air dry so that you don't have all of those heat products going on damaging your hair. Otherwise blow dry your hair by clipping up sections and using a vented or rounded brush. Comb your hair from underneath starting at your roots and working your way down. Do it this way with all of your hair until completely dry.
NEVER straighten your hair if it is wet or even slightly damp! This can and will damage your hair big time. Make sure that you have your straightener set to a temperature that works best for your hair type. For instant if you have a 25 setting straightener then for fine or thin hair use the heat setting between 1-10: pretty wavy hair, use 11-20. For the ones with thick, coarse, hard to straighten hair you should probably put it on 25. That's how I do it. Then apply a smoothing serum. Start at the ends and work your way up. I use Matrix Sleek and Shine products. Just get a little dollop because a little goes a long way with that product. It costs about $15.00 and only sold at professional beauty salons.
Sometimes your hair will have a slightly fried or burnt smell. To get rid of that add a little bit of lotion to your hair, or take a dryer sheet that has a scent and rub it on your hair. The dryer sheet will get rid of the smell and also help control static electricity in your hair. The lotion will also calm fly-a-ways.