If you aren't already riding with fenders, that's the first thing you need. Get good fenders that are plenty wide enough, and adding a mudflap to the front will make it even better.

My main piece of rain gear is a Showers Pass touring jacket. It is far superior to any other rain jacket that I have worn (for cycling). I've also got a rain cape that works wonderfully but is a bit bulky. I only grab the cape if it is really pouring. My main light is on my helmet, so it doesn't interfere.

I've tried rain pants and never been even close to satisfied. I'm going to get some of these rain chaps and hope that they do the job. I also remain unsatisfied with any cycling gloves for rain. I've got a good pair of waterproof gloves for the cold, but my hands will sweat profusely if I wear them when it is above 45 F or so.