When you start the new yarn, take your empty needle and put it in the cast on underarm stitch, ready to pick up a stitch. Then pull a slip knot through, as if you are just knitting. Instead of the regular st coming through, the loop of the slipknot will come through. That will be your first picked-up stitch. This is the way I do it for a little bit more stability on that first stitch. Some people say to just start knitting with the new yarn and tighten it up later.
So starting at the center of your underarm, you'll pick up the 2 underarm stitches, then the sleeve stitches that are on hold, then the last two underarm stitches. I would pick them up on the dpns as is convenient and then distribute them evenly to start knitting the sleeve.
I hope this is clear. I have no problem visualizing, but sometimes have trouble explaining.