Lots of good advice given thus far. I would echo the need to select your route carefully even if it adds miles (but in your case, that's probably not much of an issue.) Being conspicuous is the order of the day, being just visible is simply not enough. If you really want to try it you may have to be creative. There have been periods where I would drive in on Monday with three days of clothes to be left at the office, then commute by bike on Tues., Wed, & Thurs. and drive in on Friday. Not ideal, but at least I got three days in. I've also driven the car part way (over high speed roads), parked and cycled the last "X" number of miles. This too was less than ideal, but still better than not at all. I've also done the deal where I drove the car into work, left it there because of a planned meeting some distance from the office the next day. I then cycled home that night and back to work the next morning, drove to my meeting, went back to the office and took the car and bike home. At least I got half a commute in on those days. The point is that where there is a will there is a way.

I'd also like to address the recreation ride versus the commute. They do require different mind sets and skills. If you've been selecting you rides for recreational purposes and now are going to commute in higher traffic areas, it will take some time to adjust. However, all the "rules of the road" that you probably already know will help. Rolling stops are a probably not in your best interest; hand signals are powerful indicators making your actions more predictable; learning to take you proper place in the lane/line at traffic lights might take some getting used to, but as you claim your space, you tend to get more respect. I also tend to agree with TSL, lights are on for me day or night (part of want to be conspicuous).