How do you join a second ball of yarn
I prefer to overlap the new skein of yarn over the one I am finished with. Leave a tail of about 8in to weave in later to "lose" that end. Start knitting with both strands for about 6 stitches, then drop the "old" yarn with a tail of about 8in as well. Now you will be knitting with the new skein. This method allows maximum use of your yarn, avoids joining the new yarn on the seam edge AND is relatively invisible on the finished project. I avoid adding the new skein at the center of your work. With lighter colors or loose knits, you may notice this afterwards. The best part of this is that you avoid knots in the yarn.
I like this kind of join too. Here are a few more, about a third of the way down the page:
I use Russian join a lot as I use more non-felt-able yarns. It is easy and doesn't unravel even after a lot of washes.
I have not graduated to more wool yarns yet, so I have not tried felting.
There are a lot you tube videos on it. I just don't know how to put the links here