I think the closest thing to a tutorial you'll find is the process pictures folks are posting in this thread. Really you kind of just have to leap in, the great thing is you can't really mess up, because if you hate what you do, you can cut it up and make it into something else. You might think about taking an existing piece of clothing and adding some pieces to it instead of starting absolutely from scratch. Possibly using the gibbous technique just as trim on something like a top, skirt, or vest. Like on a skirt, you could make a bunch of ruffles from strips of scrap fabric, and trim the bottom of the skirt. Or do the same on a top or vest. Look at some of the simpler pieces at Gibbous Fashions and see if anything appeals to you that you could emulate. I've found for myself that a limited color palette helps me keep from getting overwhelmed, choosing for instance all blues, or all greens, etc.
Bonzie Designs has some tops which are gibbousy in that they have scrap trims on them, really very simple but pretty and maybe a place you might want to start: http://www.bonziedesigns.com/index2.php?v=v1
Look in the "portfolio" page for "tatter tees" - I can't seem to link to it directly.
I hope this helps some!