What do you wish someone had told you before your first commute? Four times a year I teach a workshop called "Be a Bike Commuter" for the local university's community education program.  It's mostly based on my experience and information from the League of American Bicyclists.  I am looking at making some changes for the next session and am wondering, from other experienced commuters, what things you wish someone would have told you that would have made your first few commutes more successful and/or enjoyable.
My suggestion would be:

Scout and rehearse your route before you start. 

This is really an exercise in two parts:


First part is to determine what your initial routes from home to work and from work to home (not necessarily the same, certainly not in detail) are going to be. And to work out where you're going to secure your bike for the day.
Second part is to ride the route with no time pressure "off peak" (ideal is probably on a Sunday) so that you know where you're going and you don't get surprised (lost!) when you're riding to arrive on time - it should also enable you clear up any grey areas on your planned route. As importantly, this will give you an indication of how long you should allow for the journey. If you know where you're going and how long its going to take you're going to be more able to focus your attention on riding safely and less distracted by navigation and time concerns.


Once your commute is established I'd suggest that fairly regularly you allow yourself a bit more time (much easier going home!) to explore alternative routes - especially for urban commuters. The most obvious routes are not always the best, you may find shortcuts that are faster or routes that are prettier or have less traffic or smoother surfaces or that you simply like better (or that are not really very different but allow you to vary your route from time to time "just because").