Insert needle from front to back between the last 2 stitches worked.
Wrap yarn around the needle going behind needle and around, ending with yarn behind needle again.
Pull loop through between stitches.
Place loop on the needle after last stitch worked.
Repeat as many times as needed. Begin working in the round as usual.
You can also cast on 2 extra stitches and at the stitch before the first cast on stitch, k2 tog with the cast on stitch, then again with the last cast on stitch and the stitch after the cast on stitch. This will tighten up any looseness you may have, although for tighter knitters this is minimal to unnoticeable.