Lots of people have never had a tape measure (the flexible, dressmaker type) in their hands, much less tried to actually measure themselves or someone else. I am here to tell you it is not that tricky and can be done properly, yes, by you!
The reason measurements are important on eBay: manufacturers of clothing don't always have every garment they make turn out to be exactly the right fit for the size. I have heard people complain about famous brand manufacturers of womens clothing say they purchased two pairs of pants in two sizes and they both fit!
If you are planning to buy any clothing for yourself as an adult, maternity or kids sizes above a 6, please do yourself a favor and take your own measurements, then match them up to the measurements given in the listing before purchasing. What, there weren't any measurements given in the listing??!!
OK, some people don't give measurements. I would say unless you are purchasing another of something very familiar to you, say, in the same style and size from the same designer that you already have a piece from, ASK! Most eBay sellers will be happy to provide that information to you if you ask. If you ask for specific measurements you will get the information that will tell you if the garment you are thinking about will fit you in a way that will make you happy.
Don't buy sight-unseen from eBay, measurements will make all the difference. The first thing you need is a flexible tape measure. (This is NOT a stick ruler or the kind that your husband uses in the garage).
You need to wear something form fitting like shorts and a cami for the undertaking of the measurement process. Try not to slouch or hold your breath when you are (or a friend/helper better yet) measuring, as it can distort your measurement.
Bust measurements: place the end of the tape measure at the mid-point between the breasts, this can be your starting area. Bring the rest of the tape measure around your body and back to the starting point. The place your tape measure needs to be is half-way up your breasts. Make sure the tape measure is not loose, or tight. The number where the tape measure meets the beginning is your number. If you like your clothes to fit loosely (this is called ease) you can add 1/2" to an inch. Ladies who are pregnant sometimes add an inch or two in anticipation of growth if they are in the beginning of their pregnancy.
Waist: measurements are taken the same way as explained above, place the tape measure at the smallest part of your waist and measure all the way around. A person's natural waist usually is just an inch or so above the navel (belly button).
Hips: measurements for your hip area are taken halfway between your waist and the bottom of your torso.
Length is usually measured from the place at the back of your neck where your neck meets the top of your back. When you see a length measurement most of the time it is taken from neck of the garment to the hem of the top/dress. Some people measure length from top of shoulder down to the hem of the garment. As long as the listing states where the measurement is taken from to the hem you should have all the information you need to get a pretty accurate idea of how it will fit.
Hope this helps those seeking information on measuring and measurements and how to take them properly.