Summarize this article in one sentence.
If you're looking to work on a specific project, check with your local craft or knitting store to see if they have samples made up. These samples will give you an idea of what yarn works well with the pattern and will give you an idea of how the final product will look. If your store does not have the full project completed, ask for a sample swatch instead. Craft or knitting store employees are extremely experienced in selecting yarns, as long as you know the right questions to ask. Some questions you should consider asking when selecting a yarn are: Will it stretch? What size needle should I use with this yarn? Does this yarn pill? Is this yarn easy to work with? If you already have yarn on hand but are unsure if it's the best choice for a specific project, test it out. Knit a 4"x4" (10cm x 10cm) swatch and see how it looks. To check draping, make your swatch even larger. To really test out your swatch, treat it as you would your actual clothing. Wash it, crumple it and hang it on the wall to see how the yarn reacts. If the swatch does not perform up to your standards, switch it out and try another option. Yarn doesn't have to be expensive, but using higher quality yarn will yield a higher quality project. Don't compare yarns of different materials (silk yarn will always cost more than wool yarn) but compare yarns of the same material. If you're stuck between two wool yarns, choose the more expensive option for a higher quality result. If you know what type of yarn you're looking for, check online. You may be able to score a better deal than you would in your neighborhood yarn store. Trade yarns with friends. The more yarns you try, the better you'll get at identifying quality yarns that work well for you.
Use samples to choose a yarn. Ask questions. Create your own sample swatch. Look at the price tag.