Hard to believe no one has answered this one! Humph! This is a simple one to answer. Where is everybody? Anyway, since I am a beginner and dont know your skill level, I can only give you this advice to do as I have done for myself. Get a book of crochet stitches that includes the shell stitch. I found a booklet that describes making crochet fabric using any type of stitch; look for one of those and, of course, it's nice to find a mentor! (I've found them in line at the yarn store.) Make a chain the correct size for one end of the afghan of your choice, then begin the shell stitch. Continue to the end, turn, repeat. You may have to work with each end to make the turn look good. Email me to discuss.

This is the pattern I'm using right now. I'm just using the shell stitch though.

And I'll certainly second what Quirk said about the turn stitch.

Best Wishes
Amino-X