If you are an experienced knitter you will have a feel for the starting point in your swatch sample. If you are new to knitting, follow the guide on the label of the yarn and cast on the number of stitches that you think will be at lest 4 inches. This is not an exact science; remember swatches are experiments and you are playing around with your potential project.

1. Start with 4-6 rows in garter stitch. Put 2-4 garter stitches at the beginning and end of each row and end with 4-6 rows of garter stitch. This prevents your swatch from rolling into a tube. 

2. Knit at least 4 inches of the stitch in the patter you have chosen.

3. It does not matter what size needle you need to achieve this gauge. I usually use a needle two sizes smaller than what patterns call for becaus I knit loosely. Other people need to go to larger needles. What kind of needle you use will also affect how many stitches you get per inch.

4. At the tope of every pattern there will be an area that states the gauge and that is the number you are aimng for. If you do not achieve the correct number of stitches per inch, do another swatch with smaller or larger needles. If you have too many stitches, go to a larger needle and if you have too few stitches, try a smaller needle.

5. Never measure your stitches while your sample is still on the needle. Do the entire swatch, cast off, and then measure. Leaving your work on the needles wilo distort the stitches. And, don't pull the swatch out to reuse the yarn in your project - it will be crimped and will knit up differently than the rest of your yarn.