There are several ways to add beads to your work. Here are a few ways that I've discovered.
1) I believe the most popular way to add beads is to thread them on your yarn/thread first. Then, you just pull up a bead whenever you're ready to add it. Try the Wrapped Single Crochet instead of the regular single crochet in order to ensure that the bead stays in front of your work. (Please see my videos.) When stringing the beads, dip the end of your thread (don't try this with acrylic!) in melted candle wax then form a "needle".
2) My favorite way is to crochet them in as I go. Just crochet along. When you're ready to add a bead, just slip the crochet hook through the bead, YO and draw through. This really only works with pony beads, which are just the right size for chenille. If the hook you're using doesn't go through the bead, then remove the hook and insert one that does for adding the bead. Then, go back to the other hook.
3) This is very similar to #2 above. Just remove your hook and press the loop through the bead, then reinsert your hook through the loop.
4) Buy the filament with beads already spaced on it (found in wedding and sewing departments). Crochet directly into the spaces in between the beads.
5) Buy the filament with beads already spaced on it (found in wedding and sewing departments). Sew the filament on to the last row of the scrunchie.