I had this problem when I first began, too. A good habit to get into, at least until you're past the point of knowing what's causing that and how to avoid it, is when you turn your work to begin the next row, be sure that your yarn (on the left needle about to be knitted) is hanging down. Holding the left needle horizontally, gently tug the knitted yarn straight downwards. It will help you to see your stitch better and to avoid slipping the needle in your right hand into the wrong place on the left needle.
Frequently, when I was first knitting, I picked up extra stitches especially when I made that first stitch on each row. I found that by having the yarn hang straight down, I avoided that. I no longer have to do it, now that I know where I was picking up the extra stitch.
Trust me, you will get past this stage. I didn't think I EVER would, but I did. I have a foot long practice swatch which I just kept practicing on. It looks TERRIBLE, but it does look alot better on the end than it did in the beginning.
Oh, and it also helps to be practicing with a smooth yarn (not a fuzzy novelty type yarn), as it enables you to more clearly see where you're inserting your needle.