Frogging is an unavoidable fact of a knitter's life, but it doesn't have to be slow and painful. The method I use is quick and relatively pain-free. The idea is to pick up all the stitches of the row you want to frog back to; then rip back, footloose and fancy free.
In our example, the row to which I want to frog is the black one immediately above the yellow row; however, black does not photograph well, so yellow it is.
First, notice that knit stitches look like little V's. We'll be picking up the right half of each V.
Step 1: Identify the row you will be ripping to. Find the beginning of the row. Insert your needle into the right-side of the V.
Step 2: Insert the needle into the next V.
Step 3: Continue picking up the right side of each V stitch across the row. Check periodically to make sure you are picking up stitches on the same row. With a nice colored row like this it's easy to tell. With variegated yarns, you may be able to follow the color from stitch to stitch. With solid yarns, your best bet is to look at the row below the one you're picking up and make sure it doesn't hiccup or disappear.
Step 4: You've picked up all the stitches and you're ready to rip. (Note: I'm back to black here.)
Step 5: Rip, baby, rip!
Step 6: If you were careful picking up your V's, your needle will hold your new row and you can rip back safely.
On occasion, you may end up catching the yarn under the needle or find that you accidentally moved up or down a row for a few or several stitches. For the caught yarn, you can leave it and free it when you get to those stitches. If you've hopped rows, you can transfer stitches one at a time and tink back the stitches on the higher row(s).
You can use this method for non-stockinette stitch as well, but you'll probably need to pay more attention. I've used it on lace with good success.
Hope this has been helpful!