There seem to be quite a few techniques to knit loops, so I thought I would share the one I prefer to use. This makes a single loop worked on the right side of the fabric.
How to knit a loop
Please note, these directions are for right-handed knitters.
STEP 1: Work to the position of the loop in your pattern. Knit into the next stitch, but do not allow the stitch to fall off the needle.
STEP 2: Bring the working yarn to the front between the two needles.
STEP 3: Place your thumb on the working yarn, and wrap the yarn around and over the top of your thumb, and back between the two needles. (Next time I do a tutorial I will have a proper manicure first!!)
STEP 4: Keeping the yarn wrapped around your thumb, knit into the same stitch again.
STEP 5: Allow this stitch to fall off the needle, and the loop to fall off your thumb. You now have two new stitches and a loop on the right hand needle.
STEP 6: Insert the left needle into the front of the two stitches on the right needle, and knit together.
And now you have finished your loop.
I used this loop technique to knit loops for my Loopy Sheep pattern.