You'll need whichever beads you'd like to use and a crochet hook small enough to fit through the beads. I used Debbie Abrahams Clear Glass Beads in size 6 (4 mm diameter) and a 1 mm crochet hook. You'll also need to decide which stitches you'd like to add beads to, for one of my samples I added a bead to the second stitch of every third row.
Place a bead on your crochet hook.
Once you've knitted up to the stitch you'd like to add a bead to, insert your crochet hook into the stitch - taking it off your knitting needle.
Slide the bead down your crochet hook and onto the stitch.
Place the stitch back onto your needle and remove the crochet hook.
You can now simply knit into this stitch and continue knitting your I-cord until you need to add another bead.