I have quite a few projects lined up so I decided I would swatch for all of them at once, that way when I am ready to start a project I can just cast on assured that I got the correct gauge. As I was knitting all of the swatches I thought about how my swatching process has evolved since I was a newbie knitter and I also thought I would impart some of my experience and wisdom here on the blog.
When I first started out knitting, I will admit, I didn't like to swatch - at all. It just took time away from me getting right to my project. It was just a waste of my time. I would make a swatch anyway - but not very well. This might account for the fact that some of my sweaters don't fit the way I would really want them to. I would cast on the exact number of stitches stated in the pattern and then knit for an inch or two, measure and if everything looked ok then that was the end of the swatch. I might have even frogged some of my swatches at that point to save yarn. I'm pretty sure that yarn amounts stated in patterns include yardage for a gauge swatch.
Over the years I've learned a thing or two - especially that a gauge swatch is very important. It is an absolutely essential part of the knitting process if you want something to fit accurately. Now I make sure to knit a correct swatch. I cast on the number of stitches stated in the pattern to four inches. Then I add four stitches on either side - two for a garter stitch border and then two for a little bit of wiggle room. The first and last four rows of the swatch are knit in garter stitch. I put a garter stitch border on the swatch for two reasons: First, so it won't curl up too much, and Second, it gives the swatch some structure, which I feel the stitches need, especially if you are going to be knitting a sweater. The next step is important: Block your swatch. I know this takes extra time but you are likely going to be blocking your finished knit and this will tell you the correct gauge. It will also tell you how the yarn will bloom and what it will look like after blocking.
After the swatch is dry, I unpin it and let it rest for a little bit before I measure. I put t-pins in to mark the amount of stitches stated in the pattern. If it comes out correct then you can start your project. If not, then its back to the drawing board. If you have too many stitches, you need to go up a needle size. If you have too little stitches, you need to go down a needle size. Don't forget to measure the row gauge as well. Row gauge is important in patterns that specify how many rows need to be knit to get the correct length of your garment.
Swatching in the Round
Some sweaters are knit in the round. Your gauge will be different for knitting in the round than knitting back and forth so you will need to swatch in the round. This is super simple. You will need a circular needle. Again, I cast on the number of stitches specified in the pattern to four inches and then add 4 stitches on to both sides. After knitting a row, slide your swatch back to the beginning of the needle so that you are ready to knit again. You will have to carry a length of yarn behind your work. I don't work any garter stitch borders on a swatch knit in the round. Just be aware that the end stitches will be loose and you will have to tug on them to keep them in shape. Your swatch will look something like this while knitting:
(I apologize for the dark yarn but I am knitting a black sweater in the round so this is the only swatch I have to show for the time being. I hope it isn't too difficult to see.)
After finishing the swatch, I bind off and cut the floats in the back of the swatch up the middle and the block it. You can then cut the excess yarn on the sides to tidy it up. Then its time to measure.
One last tip is to make sure your swatch is knit in the correct stitch pattern that the pattern states. If it is stockinette, then swatch in stockinette. If it is in a cable pattern or in a fair isle motif the you will need to swatch accordingly. I hope this helps and just remember that a gauge swatch is an integral part of your project. Don't skip it!