Gauge:
Granny squares can be worked at any gauge.
If you're crocheting a granny square as part of a pattern, match the gauge mentioned in the pattern as closely as possible. Otherwise, you can work your granny squares at whatever gauge you like.
Choosing Materials:
Granny squares can be worked with any yarn plus a crochet hook of appropriate size. Check the label on the yarn you plan to use; the correct crochet hook will be specified. Use that as a starting point, but feel free to make adjustments as needed.
Choosing Colors and Fibers:
Granny squares can be a single color or multicolored. Any combination of colors can be used. There are infinite possible variations.
If you work with multiple yarns, the fiber contents should be the same, or compatible, so that the finished project will wear evenly with repeated washing and use.
For example, do not combine cotton and acrylic in the same granny square. The cotton and the acrylic will wear differently. Acrylic is typically shrink-resistant, but cotton can shrink significantly when washed. Using these fibers together could result in a project that looks fine before washing, but distorts during the washing process.
Pay attention to care instructions, and make sure that all fibers used in the same project can be cleaned using consistent methods. For example, do not use "Hand wash only" yarns in the same granny square with "Dry clean only" yarns.
Abbreviations:
ch = chain, chs = chains, st = stitch, sts= stitches, sl st = slip stitch, dc = double crochet
