I flatiron my hair with my Sedu iron(which broke on me the other day).
I usually wash, deep condition, put on a leave-in and sit under the dryer. When my hair is dried, I take a tiny part, put serum or whatever on it, make sure it's combed and tangle free...then I take a brush and pull my hair with the brush from the roots with the flat-iron following right behind it. THIS gets my ends straight.
The whole brush thing may be a little controversial since I'm sure some may see it as damaging, but I on;y flat-iron my hair once or maybe twice out the year.
i just usually wash my hair, let air dry , then flat iron with my chi iron. sometimes i dont use products ( i know i know... ) sometimes i use chi silk infusion.
i use the comb chase method to get my hair straight. ( comb follows directly in front the flatiron to ensure straight strands. )