I've never done this before. Any tips? It seems difficult.
Hold the two strands together as though they were one and start knitting. That's all there is to it. You may need to knit a bit more slowly than usual to make sure you catch both strands with the needle on every stitch.
Some people wind both strands into one ball but I don't think it's worth the trouble.
The yarns will try to tangle on each other, but all you have to do is move the balls around every few rows to keep it from getting bad. Like was said above, it's much easier than it seems. If you can knit with one strand, you can knit with two!
Something I do when I knit with two strands--I get a couple of large ziplock freezer bags and cut a corner on the bottom of each one. I put the yarn in and feed the strands of yarn through the corner, and then seal the bag up. It helps to keep them from getting tangled up.
if I think far enough ahead, i put them in the same bag with a hole in each of the two cornersthen I just spin ONE bag to untanglebut for the most part I DO wind a single CPB with both yarns at oncejust stack them on ur swift and wind away