Trading Risk Management: How Much Money to Use Per Trade?

There are many opinions and definitions out there regarding the amount of money you should be putting into a trade compared to the size of your trading account. Some say no more than 5%, others say slightly more or even less. I won't call some of these definitions wrong, but there is an aspect of practicality that must come into play and be considered in order to assure you are being wise about your actual position sizing.