To blow dry my hair straight...
I put coconut oil on my hair when wet.
When it's mostly dry I apply a cream heat protector and blow dry in sections using this hot air brush (Babyliss Style and Shine):
I only use the round boar bristle attachment.
I clip up completed sections in a twisted bun type thing to avoid it frizzing up or getting mixed up with the uncompleted section.
This will make my hair fairly straight, BUT it will frizz really easily unless I follow by flat ironing. I do this in sections (again), using a spray heat protector on each section before straightening with my (in need of replacement) ceramic coated wide flat iron. I clip the sections up in the same way as after blow drying.
When it's all done, I'll apply a serum to, you guessed it, prevent frizzing.
Sorry about the essay! [size=-2]Can't wait til I BC and don't have to deal with this![/size]