After doing about a hundred afghans with the afghan stitch (tunisian); I have come to these conclusions...
1. For the beginning chain, use a regular hook that is two or three sizes larger than the afghan hook you intend to work with.
2. Begin using the afghan hook starting with row one.
3. Sometimes you can go up a size or two with the afghan hook and still be on the gauge. Not always. Refer to step one and two.
4. Relaxing with the afghan stitch is vital to your physical and/or mental health. Take a deep relaxing breath. Take a nap. Take a walk. Drink a beer. Take a pill. Whatever you do, relax. Otherwise you will experience great pains in your arm and shoulder that will keep you tossing and turning at night until you finally get used to working so hard and being so tense. Remember that it is supposed to be fun. Relax and be nice to the dog again. It’s not his fault you want to do something awesome like the afghan stitch.
5. Smile! When your afghan is all done and the compliments start pouring in, grin and bear it. Say "I know" and "Thank you!" Don’t point out all your flaws and mistakes. If they can’t see it, let it go. Pat yourself on the back because you earned it. And be proud of your accomplishment. You deserve it.