Even the most experienced knitters can drop a stitch. While, you can unravel your bind-off and pick those stitches back up before correcting a dropped stitch, it's not absolutely necessary to do that. With a little practice, there is another traditional way to pick up and hide a dropped stitch.
Things You'll Need
Spare yarn or thread
Locate the dropped stitch in your work. It is the tiny loop at the base of the ladder of dropped stitches running down your work. Insert a small crochet hook--size US F works well--into this loop from the front to the back with the ladder of stitches behind the loop.
Grab the first horizontal ladder rung with the hook and pull it through the dropped stitch from back to front. Release the original loop and keep this first picked-up stitch on your hook. Repeat this process until you have picked up all of the horizontal ladder stitches and your dropped stitch is now lined up with your bind-off.
Pick up a stitch from the bind-off, if you can, and pull it through the loop. If not, simply hold the dropped stitch adjacent to the bind-off stitches and temporarily release the crochet hook.
Thread a spare length of yarn or matching thread onto an embroidery needle. Weave the end of this yarn in and out of your knitted piece on the back side to secure and anchor it.
Remove the crochet hook and insert the embroidery needle into your dropped stitch from back to front and pull the yarn all the way through it. Wrap the yarn back over the top of the dropped stitch and weave it in and out through the stitches on the back of the piece. This tacks down the dropped stitch and keeps it from unraveling again.
Cut off the excess yarn and remove the needle.
This describes how to pick up stockinette pattern stitches. To pick up purl stitches you have to pull the ladder bar through the dropped stitch from the front to the back instead of back to front.