If you’re shooting in the rain (you did make sure that you camera is going to be water-tight or you’ll need to perform an immediate drying maintenance after shooting), one of the things to consider is — do you want to see the raindrops or not? While this is not always possible unless the rain is heavily falling, but if it is, you can stop the rain (and thereby see the raindrops) or have the rain be a blur, more like a semi-opaque curtain that’s laying awash your entire image.
To stop the rain, you need to have the shutter speed cranked up fairly high (at least 1/250, and that might not be enough). However, at that shutter speed–and considering that your main light source’s power is reduced by the cloud cover–you need to set the aperture so you can achieve a fairly deep depth of field… otherwise only your subject will be in sharp focus, and then the point of the image will be diminished.
Now maybe your cup of tea is to use the falling rain as means to add additional soft focus to your rain-drenched background. This is easy to achieve as well, all you need to do is drop the shutter speed to maybe 1/30 or 1/15 (so you might need a tripod, monopod or learn how still your body enough to avoid camera shake on these lower shutter speeds), and open up the aperture to a fairly wide f-stop (where the DOF is shallow; time to use the DOF preview button).
Once you’ve decided on how you want to portray the rain (while it’s raining), you can fire away with reckless abandon or carefully calculated skill and measure. Controlling the DOF is critical for creatively using the falling rain in your photos, and adjusting your shutter speed and aperture to effectively manipulate the DOF requires practice, practice, practice. Good thing you’re working in the digital world, so you can see your attempts immediately. However, if you’re not gone fully digital and still enjoy the physicality of working in film, shooting in the rain requires thinking out your shots and all the elements that go in to making up a shot carefully ahead of time.
The beauty of shooting just after the rain is that when most objects are wet they glisten and the water bends the reflected light coming off an object’s surface. You must take advantage of this, because something as simple as wet pavement provides a glowing sheen that will elevate a perhaps mundane photo and increases the apparent depth of any image… why is that the case? The water reflects the light (whether it’s the sun, headlights or sodium vapor municipal lighting) in multiple directions and intensities and this optical phenomenon gives distinctive and definitive shape to whatever happens to be wet and falls within your line of sight. When angling yourself for your photo and seeking that “sweet spot” shot, see if you can have the light reflecting off the wet surface(s) aim directly into your lens.
When you’re done shooting in the rain, be sure to wipe down your camera, dab the lens dry with lens cleaner cloth and detach the lens from the camera during the drying process.
