I had this issue when I first started. I'm sure if you keep doing what you're doing they would get better, but I didn't want to wait that long. I always, ALWAYS use slipped stitches to make nice even edges. (Unless those stitches are used for shaping or something in the pattern.)
theres a few different ways to do this, but this is my favorite:
On the first stitch, bring the yarn to the front and insert your right needle into the st as if to purl, but slip it instead. Work the row per your pattern, and KNIT the last stitch (of every row.)
Like I said, sometimes you can't do this if the pattern calls for those stitches to be worked in with the pattern, but if you want you can always add 2 sts to be saved just to make these nice edges.