A-hem. Some of us are more coordinated than others. Some of us can manage close, detailed handwork, and some of us were made for other work, but not sewing.
Truth is, though, even a bumbler can learn to finish a hem -- at least a simple, straight, unlined hem. Hemming requires some very uncomplicated stitching, which could be picked up from a sewing book. If you think your interest in sewing might endure, consider buying a complete guide to sewing, like Vogue Easy Sewing, (Harper & Row, $17.95), or enroll in one of the hundreds of sewing classes offered in the area. If you want to learn just enough to shorten a straight skirt, get a slim, simple guide with plenty of diagrams such as The Perfect Fit, or Clothing Care & Repair (Cy DeCosse, $11.95 each), both part of the Singer Sewing Reference Library.
Most sewing machines these days come with an invisible hem-stitch option and well-diagrammed operating instructions. There might be an even easier alternative, though. Garments, like sportswear or top-stitched skirts and dresses, can be machine sewn with a regular straight stitch. It's as simple as sewing a straight line.
Another alternative for lazy people is fusing a hem. This requires no thread, no needle, and virtually no ability -- only an iron and double-sided iron-on interfacing.
Nothing looks worse than a badly done hem -- when the stitches make deep pinches in the fabric, or when the hem is so deep and thick that it makes the garment hang oddly. Also, changes in hem length can dramatically alter the proportions of the skirt or dress.
Among other things to keep in mind when hemming on your own:
Find very closely matching thread.
When fitting the hem, wear all the undergarments and belts that you would normally wear with the garment -- they might change the hem length.
Have someone else -- a reliable person with good eyesight -- mark and pin your hemline, measuring from the floor up with a yardstick, so the edge is the consistent length from the ground.
Press the hem before sewing it.
Never pull the stitches tightly as you sew. If the fabric is bulky, use hem tape.
Leave some ease in the lining to be attached to the garment -- so it doesn't pull the fabric under.
Use an invisible stitch -- a slip-stitch, a hemming stitch or blind-stitch for all hems unless: 1) it is sportswear and you don't mind cutting corners. 2) the skirt or dress is already top-stitched. 3) you are lazy and don't mind being laughed at.