One key to fixing mistakes in your knitting is being able to determine that there are mistakes in the first place and where exactly they are. And to do that you have to be able to read your knitting.
Reading your knitting simply means that you know what a knit stitch looks like on the needle and in the knit fabric as well as a purl stitch. When you're no longer a beginner, it will mean you can tell a knit 2 together from a slip, slip knit, you know what a yarn over looks like and so on.
Being able to read your knitting makes it possible for you to follow instructions that tell you to knit the knits and purl the purls, but it also allows you to see mistakes in a pattern stitch and be able to fix them.
If you don't already know how to read your knitting, start small. Look at a swatch of ribbing and notice what the knit stitches look like compared to the purls, both on the needle itself and down in the knit fabric. Maybe mess up the pattern on purpose so you can see what a stitch pattern mistake looks like.
This is such an important skill in knitting that it's worth taking the time to pay attention to what your knitting looks like so you can spot and correct problems more quickly and easily.