My first commute to work (after having bought the bike 2 weeks prior) ended with me riding home in the dark, while pouring rain came down and in rush hour. It was nerve wracking but like it has been said in previous posts just make deliberate smooth motions when turning, changing lanes, stopping and accelerating. The poor visibility makes you more aware of the cars around you because if you're visibly impaired then so are they. I made sure to pump my brakes when stopping so that the brake lights would go on and off thus making me visible to cars behind me. My gear kept me dry and warm so I did not have any distractions due to comfort. Take it easy, slow and relaxed.