Harry, a picture would be ideal, but without one (and because I'm terribly procrastinating today!), here are some general guidelines from my own personal experience:
1) Shorter skirts tend to work best on those under 35; this is a general guideline. I still wear shorter skirts every now and then when I get the whim, and I'm 43, but I tend to wear them with opaque tights, as the skin on my knees aren't so young looking these days.
All in all, if you are over 35, - or any age for that matter - the universally flattering length is at or around the knee. This could be just above the knee, which is a good alternative to shorter skirts and might be a safe place to start?
2) Anything shorter - make sure to do the "bend over" test when you are in the dressing room. Ensure that when you bend over, your panties aren't showing. I have found that this can happen with skirts only 3-4 inches above the knees - depending on how they are cut. It happens more often since I passed my 30s; I think because my butt has slid towards my knee.
Also sit down to ensure the skirt doesn't ride up too much. Check the front view when you are sitting to ensure you aren't flashing anything. Cross your legs, move around, etc. And pay attention to whether there is any fabric left under your derriere when you sit! This is the biggest drawback to short skirts, in my experience, and another reason I opt to wear tights with them.
5) Shorter skirts work best with flat shoes, or a very small (no higher than 1 inch) kitten heel. Anything higher, and you run the risk of looking tarty, in my humble opinion. Besides, if you are worried your legs are too skinny, adding too much heel will make them look even more so. Whereas a ballet flat or flat boot looks adorable with shorter skirts, and strikes the right balance.
6) With any skirt, you need a "skirt-length" top. Angie has blogged on this topic in the past - do a site search. This is even more important with short skirts, to get the proportions just right.
7) If you're going to show a lot of leg, then go more conservative and demure on top. A turtleneck, if you can wear those, is an adorable look. No plunging necklines or too much exposed skin. Let your legs be the star!
8) As an alternative, consider trying a tunic dress-over-skinnies look. This has also been blogged about. Unfortunately it is difficult to find knee-length dresses so wearing the ubiquitous short dress over skinnies is a good and fashionable option.
Hope that is helpful!
