The best way to work in ends is with duplicate stitch on the wrong side of your work. To make it even more invisible on the right side, you can split the stitches, called skimming, as you work in your tails.
I use this method because it is the most invisible; it allows the fabric to drape without pinching or pulling up; and it is the least likely to come undone. Yarn that has been worked in using the figure eight path of duplicate stitch has a much harder time slipping out than yarn worked on a diagonal or mostly straight path – or, God forbid, knotted!
In the example below I used dark yarn for the duplicate stitch to make the instructions clear. You will be working your duplicate stitch with your sweater yarn.