I was asked an excellent question in the comments yesterday: Do I have a skirt length philosophy for myself?
Yes, and so should you. Not carved into stone, but you should have a general idea of what hemlines look best on you.
Things to take into consideration: Your legs. Everyone has a "best hemline" for her legs. Usually she has two - one for knee and one for ankle. You might also have a best thigh hemline, if your age and weight suit a miniskirt. (My "knee" and "thigh" hemlines are about the same place).
Modesty and Function: Are you going to be running after toddlers on a playground? Go long. Not so long that you trip over the hem, but more than long (and full) enough that you can touch your toes at a moment's notice without a wardrobe malfunction.
Overall proportion: Just because a hemline looks good on your knee, doesn't mean that a knee length skirt looks good on your body. I took the following picture a few years ago. I made the modifications with the picture program that came with my computer - a few properly colored rectangles. But take a look at the difference just a few inches can make!
In the first picture you can see that the skirt could maybe use an inch to look better on my leg, but the overall effect of a calf-length skirt on me is very dowdy. Likewise, a dropped yoke is only making my full tummy and lack-of-waist more apparent. (And take this time to think about fabric - adorable as the rainbow flowered denim is, it's certainly making this look *very* homemade).
In the second picture I've dropped my neckline by perhaps an inch - certainly nothing extreme or immodest. More importantly, I've widened it and squared it off, which gives the illusion of a slimmer neck.
The skirt's "waistband" has been raised and trued to my waist. Also, I dropped the hem to high ankle length. Result? Visually losing about 5lb overall. I have not changed this picture except for the colored boxes! Taller, slimmer, dressier - with very minor changes in proportion.
And this is when I stopped sewing calf-length skirts and went to ankle-length.
And this is a great shot of overall body proportions. Here I have gone with my best silhouette in both pictures. In the first, I have a different colored skirt and top. I am visually chopped in thirds (because you can also see my leg from the knee down). On someone 5'2" and wide? Not great!
The second shot is my favorite dress. Same hemlength. Same style. But all one color - and again, you can see how I am visually losing weight, even though my waist isn't substantially reduced from one picture to the next.
The commentor said that she's tall. If you have more real-estate to work with, you might do very well with two colors or a knee-length skirt. Tea-length is a *gorgeous* length on many women... I can't wear it, but I wish that I could!
Take some pictures of what you already have and play with them. It's easy and fun - and will give you a lot of ideas for your next shopping trek.