It's VERY simple: If there are three available urinals and I'm using the left-most one.... DON'T USE THE ONE NEXT TO ME!!!! Start at the right!

The rule my friends and I always called the "1 5 3" rule. If there are 5 urinals, the proper order to fill them is 1, then 5, then 3. Then you start filling in 2 and 4 if absolutely necessary.

It gets a little complicated when there are 3 toilet stalls and the one on the far side is one of those handicapped jobs. They're uncomfortable for a lot of people to sit in because you're on a giant throne, plus it's always good to save that one in case an actual wheelchair person comes in. (This has never come into play in my experience, however.) So with this setup (like we have at work) a lot of people who would normally take crapper #3 when crapper #1 is in use decide to take crapper #2 instead. So #1 becomes the most sought-after location.