(The consumer trend lately has been to buy teeny weeny mittens and gloves which stretch to fit, and cost only about $2 per pair. The big problem with these mittens and gloves is that they don't actually keep your hands warm!)
Mittens also provide the potential for endless variety. You can try out different stitch patterns (on the back only, please - no one likes a weird stitch on the palms of their mittens), stripes, different yarn types, colors, and construction types. Much more so than many other knitted gifts, mittens are interesting for the knitter to knit, and useful for the recipient to wear.
The best way to learn how to knit mittens is to start with a basic pattern. Many knitting accessory pattern books include a mitten pattern. I have had some success with the basic pattern in Ann Budd's
Knitter's Handy Book of Patterns. (But I have had some failures, due to row gauge problems.) I also like the basic mitten patterns in Claire Crompton's The Knitter's Bible: Knitted Accessories. There are several free stand-alone mitten patterns out there, too, like Mrs. Roosevelt's Mittens and Midge.
Mitten Knitting Notes
* You may be intimidated by the thought of knitting mittens out of sock yarn. All those tiny stitches! But sock yarn is a nice weight for a pair of mittens, whereas a DK or worsted weight yarn can sometimes be too bulky and hot. And sock yarn means the mittens will be machine-washable!
* Most (maybe all) mittens are knit from the cuff to the fingers. Be sure to use a loose cast on when you start, so that the cuff is comfortable. I typically cast on my stitches over 2 needles held together.
* You want the cuff to be ribbed, to help snug it up. A 1x1 or 2x2 rib is standard. However, a twisted rib can look quite nice as well. To make a twisted rib, do a 1x1 ribbing but knit each stitch through the back loop (ktbl).
* The thumb gusset can be a little intimidating to new knitters. But it's just a place where you increase regularly. No special magic! Just set a stitch marker, and increase as the pattern specifies.
* Some patterns have you slip the thumb to waste yarn, and cast on stitches to cross the gap for the rest of the hand. Other patterns have you knit with the waste yarn then go back later and snip that thread to pick up the thumb stitches. I greatly prefer the former. For one thing, it allows you to try on the mitten as you knit. For another thing, I have never really perfected the art of gracefully snipping the waste yarn and picking up all the stitches correctly.
If you develop a preference for one technique over the other, know that you can use that technique for almost any mitten pattern, regardless of what the designer specifies.
Photo credit: Flickr/AnnaKika