There's the waffle weave stitch and then there's the waffle weave technique. Why are there two things with names so similar? To drive us all mad, but they are actually rather different. The stitch (sometimes known as the basketweave stitch) is all post stitches. The technique is all sorts of weird unused loops and front loops. So, to begin:
1) Chain however many chains you want plus one, which will be the turning chain.
2) Do your best single crochets in each chain starting in the second chain from the hook. Chain one, turn.
3) Now, the tricky row...insert your hook in the unused loop from the foundation chain and the front loop of the first row 1 single crochet. Yarn over, pull up a loop, yarn over, pull through two loops and you've finished a single crochet, waffle weave style. Repeat across.
This will get weird. Keep track of which side is the top and which is the bottom. It's on this row that you will get confused.
4) Chain one, turn. Insert hook in the unused loop of a row 1 single crochet and the front loop of a row 2 single crochet. Pull up a loop, complete a single crochet. Repeat.
5) Repeat until you have your super dense fabric.
There are more pictures here because I'm not quite Flikr savvy yet.
Although, if I'm completely honest, I like post-stitches more.