Hand sewing is an important skill and the ability to mend garments by adjusting hems, sewing on buttons and darning small holes, can be a good way to save money by making clothes last longer. I was lucky to learn to hand sew by doing cross-stitch as a teenager, which involves learning to make small neat stitches. My mum taught me to hem when she got sick of adjusting my school uniform skirts as fashions changed. Since then, I have been able to adjust hems as required. I'm tall, so I often extend hems on trousers, and skirts can go either way.
First step is to unpick the hem (or as often happens in cheap clothing these days, it will come apart before you have a chance to unpick) and decide what length hem you want. Then iron, measure and pin the hem. (Ironing is a pain, but its worth the effort for a neat finish).
Here's a hem that came apart ready to sew back together
Next, choose some thread as close as possible to the colour of your garment. Thread a needle and tie a knot in the end of the tread (I make a knot in the fabric, but I couldn't find that on youtube, so it might be just my weird way of doing it, maybe I need to assume that you have a basic sewing ability here, if not, go and practice some cross-stitch first!). Start at a seam (so that you can hide the knot) and work around the hem in "blind stitch". The idea is to pick up a tiny stitch on the "good" side of the fabric every half inch (centimetre) or so, and create a large stitch on the inside. Work all the way around and tie off the thread where you started.
If you have a full skirt, you will need to make a small tuck as you work around so that you get a smooth finish.
These trousers were too short, so I had to make a very narrow hem
This isn't the easiest technique to explain in a blog post, so you might want to also watch this excellent youtube video, particularly from about 2.30 minutes onwards.
Do you hand sew? Do you adjust hems to suit your height or fashion? Any tips?