One of the perils of online shopping is the inability to try things on.  You're just not sure whether the item will fit you or not.  As I've mentioned before, knowing your measurements will alleviate much of that fear.  Never trust sizes - they're never the same between designers and stores.  But it's very rare to find a shopping site without a Size Guide.  Clicking on this handy little link will give you a chart (like the one pictured here from Banana Republic) outlining the basic measurements associated with that item.  There are usually specific size charts for jackets/outerwear, blouses, dresses/skirts, jeans/trousers as well as for regular, tall, petite, and plus.

Now, it's easy to measure your own bust, waist and hips in front of a mirror.  But any kind of length measurement without help is much harder.  Bending over to look at the tape measure obviously doesn't work.  Pressing the tape along your body almost always results in a wrong number.  But here's a little trick to determine if the length of an item will suit you or not.

Grab a flexible tape measure (these are dirt cheap at fabric stores!) and a small metal binder clip.

Fasten the binder clip onto the tape measure so that the little arms are directly over the desired measurement.  Now head to your full-length mirror! 

Say you want to know where a skirt that measures "21" from natural waist" will hit you.  At the knee?  Above the knee?  Just hold the 0 end at your natural waist and let the tape measure hang.  The binder clip provides just enough weight for the tape to hang straight and the little arms show you right where the 21" will be.  And because the tape is hanging, like the skirt will, you get an accurate measurement over your stomach and hips. 

This works with dresses and pants as well.  Try it and take advantage of that free-shipping a little more confidently!