Firstly, I get all my crochet block patterns from this wonderful book, 200 crochet blocks for blankets, throws, and afghans by Jan Eaton.
This book has taught me so much about crochet and the patterns are all so clearly written and easy-to-read! There are illustrations in the back that show how to make each crochet stitch mentioned in the block patterns. From this I learned how to make Popcorns, Bobbles, Puff stitches, and Triple and Half-double crochet stitches. (SO much fun!)
These are some of the patterns in this book.
Ok. First thing I do when starting an afghan is to make a plan. I choose what size I want my finished afghan, and what crochet blocks I want to use in the afghan. I draw up a diagram like so... (Sometimes I take the time to use a ruler and make much straighter lines) This diagram below was hastily drawn in a moment of frenzied creativity... :D
And here we have one of my typical crochet blocks. I use an H/8 size hook, and regular worsted weight (4-ply) yarn... sometimes mixing in some baby yarn here and there... and since I've discovered I crochet with such a large (rather loose) tension my crochet blocks all come out about 8 1/2 to 9 inches.
When creating your afghan, make up a 'test block' and then multiply the dimensions to whatever size you want the finished creation to be and calculate how many blocks you'll need.
To piece the blocks together, I lay them out in the order I want on top of a solid-colored surface (i.e., a white sheet on top of my bed) and pin them in place, for a large afghan. I sew the blocks together, row-by-row, with coordinating yarn and a large plastic needle. I use a whip-stitch sort of technique... ah, might have to post pictures of that later so you know what I mean.