Start by tying a slip knot, leaving a 6 inch tail. The loop of the slip knot should be just over 2 inches.
Create a chain for the first row of your blanket, working toward the right. Make the chain as long as you'd like the blanket to be wide, then add one more loop.
Start working toward the left for row two. Skip the first loop, then pull a loop (knit stitch) from behind through the second loop.
Continue pulling a loop from behind through every loop (hole) in the chain. Make sure all the loops you create are the same size, just over 2 inches. When you get back to the knot, pull a loop through the knot as well.
Start working toward the right for row 3, pulling loops from behind the same way you did in row 2. Every time you start a new row, skip the first loop. Every time you end a row, make sure you work through the skipped loop from the previous row.
Continue working back and forth until the blanket is as long as you'd like.
To join a new ball of yarn, tuck the tail end of one yarn inside the tail end of the other yarn. Sew together with a needle and thread. (If you're using chenille yarn you can just tie the two pieces of yarn in a tight knot and trim the tails.)
When the blanket is as long as you'd like, cut a 12 inch tail. Starting from the other side, bind off the top, then thread the tail through the last two loops and tie a knot. Weave in the tail, then use needle and thread to secure it.