Never having done this before I decided to take some advice. Not having anyone to ask (directly, that is) I googled for trouser hemming. One of the links that came up said to stand on a stool and get a friend with a ruler and some pins to help you. Then it said this...
"No matter what length you decide you want your trousers to be, the bottom edge of the trousers should always be the same distance from the floor all the way around your leg - you can make sure of this with the ruler."
Now I'm no expert but that just doesn't seem right. When I wear a pair of trousers that in my view fit, the front part of the hem drapes over the top of my foot and the back part of the hem is in line with the top of the heel of my shoe. The difference between the front and the back might be as much as two inches depending on which shoes I'm wearing.
See photo in Gallery that demonstrates this.
The only way that the hem will be the same distance from the floor all the way round is if there is absolutely no drape over the front of the foot at all. Trousers that short would just look silly, right?
If anyone's interested, the advice came from a BBC website, here: http://www.bbc.co.uk/dna/h2g2/A209008
and I can't make up my mind if they are being serious or not.