What I usually do is part my hair in four sections. But not the way most people do.
1)I make one part in the back of my head that goes from the middle of one ear to the next. I clip that section or use a rubber band.
2)Then I make a nother part across the top of my head from the top of each ear. I clip that section too.
3)Then I split the middle section in half vertically. I put the right side of the middle section in a rubber band and leave the left section out.
4)I start straightening my hair on the left half of the middle section parting accross my scalp horizontally. I create sections of hair that are 1/8-1/4 inch thick and about 3 inches wide. I clip the hair up that I'm not straightening using hair pins. Gravity works in my favor as well and keeps the hair on top out of the way.
5)I work my way to the middle of my head and then do the other half of the middle section.
6)Then I do the back. I section it in to three sections vertically. Then I start at the nape of my neck and work up, straightening small sections at a time.
7)I straighten the front just like I straighten the middle.
I keep each section in place with clips until I'm done. This usually works really well and goes much faster because I can see what I'm doing. Hope this helps. I put a really simple pic in here to show you what I mean.
As for temp. You want to use the lowest temp. possible that will still straighten your hair. Practice on section using a slightly higher setting than last time. If it comes out ok then stick with it... if it is too low...go up a notch and try again until you find just the right setting.