Collect a soil sample
The ratio of sand, silt, and clay in soil determines its ability to hold moisture and nutrients. The test I use to determine a soil's texture is a low-tech alternative to sending a sample off to a lab. All you need is a straight-sided jar with a tight-fitting lid (an empty peanut butter jar or mason jar works well), some powdered dishwashing detergent, a ruler, water, a calculator, a soil sample, and a soil texture triangle.
A soil sample should be representative of a gardening area. If the soil in the area I'm testing is fairly uniform, as in a raised bed, I take a sample from the middle of the bed. If the area I'm testing is large, like a lawn, I make a composite by collecting small samples at evenly spaced intervals across the area. I then mix these small samples together to form a representative sample.
To collect an accurate sample, containing soil from where the roots actually grow, I scrape away the first two inches of soil and dig a hole 6 inches down. I place a trowel full of soil (free of large organic matter and rocks) from this hole into a plastic bag and label the bag with the soil's origin. This is especially important when I'm collecting a number of samples.
The soil must be sifted before testing, so I spread it out on an old cookie tray to dry for a day or so. Once the sample is sufficiently dry, I sift it through a wire-mesh sieve or an old colander to remove small stones and roots and to break down any lumps of soil.