One thing that I have learned both in knitting and crochet and swatch, swatch, and if still not sure swatch again. What I do with those swatches depends on the yarn and if the flat or in the round.

Flat: I make them big enough to be an afghan square or a dishcloth depending on the yarn of course.

Round: These can be turned into sachets or into a small carryall to be used when out on the town or at the farmer's market, when all you really want is your wallet, keys, and cell phone.