See http://csscomb.com/about/. I think the order is configurable. Sorting helps readability and it helps you find the properties easily as your eyes get tuned to where they are usually found.
This is probably most effective if you tend to specify the same values for the properties as well, so that a run can extend from one property name through its value and to the next property name.
Clustering properties with identical prefixes will provide some improvement by itself, as it can keep the 'backward distance' values used in a small consistent range, but I expect that's going to be a much smaller effect.