New knitters often have the problem of increasing stitches along the sides of their work without really realizing what's going on. There's one common incorrect way of starting a new row of knitting that can easily cause a knitter to mistake one stitch for two. Here's how not to start a new row of knitting if you want to keep your edges -- and stitch counts! -- even.
When you get to the end of the row, the needle with the stitches is in your right hand and the empty needle is in the left. To keep going, of course, you turn the knitting over, switch the needle with the stitches to your left hand and the empty needle to your right and keep on knitting.
The potential problem comes with how you hold the working yarn when you start knitting that first stitch. On knit rows, the yarn is at the back, but you have to be careful to bring the yarn to the back under the needle rather than over it, which is the way shown in the picture.
If you bring the yarn to the back over the needle, that pulls the first stitch of the row up, so that it looks like two loops on the needle instead of one. If you knit into both of these loops, you've just increased and might not have even realized it.
Instead, make sure you bring the yarn to the back from below the needle. To be extra sure you're only knitting the stitches you're supposed to, give the work a little tug before you get started so you can see that there's only one loop on the needle for the first stitch.