Here in the northern hemisphere, the shortest day is fast approaching and whether we like it or not, much of our photography will be of the low-light variety. We've put together some suggestions for coping as best you can when things are a little dim and the light with wish you wish to draw is a scarce commodity.
Look for the light
This might sound terribly obvious, but it's a fundamental of photography: look for the light in your scene and use it to your advantage. Use the light from streetlamps, from candles, from the moon to illuminate your subject—even be the subject—and create interesting shadows in your photos.
Do not be afraid of high ISO
While a too-high ISO can be responsible for noisy, grainy photos, advancements in sensor technology mean that it's possible to push ISO much higher than was previously acceptable to get the shot you want. Remember: a little grain can be better than motion blur; if you shoot in Raw, images can be cleaned up; a black and white conversion can produce noise-negating miracles.
Open up your aperture
The wider the aperture you select, the more light you'll let onto the sensor and the faster shutter speed and lower ISO you'll be able to use. This will of course come with the caveat of a shallower depth-of-field, but that can be applied creatively.
Watch your shutter speed
A slower shutter speed will permit more light to reach the sensor, but it also has the potential to introduce motion blur if it isn't sufficiently fast to freeze the action in your scene, as well as camera shake if you're hand-holding your camera. Sometimes, however, motion blur contributes to the story that you wish to tell, so don't dismiss it entirely.
Consider a tripod
The general rule for hand-holding a camera is that you shouldn't do it if your shutter speed dips below the inverse of the focal length of the lens you're using. Thus, for a 50mm lens, you shouldn't attempt to hand-hold your camera using a shutter speed slower than about 1/60 second. If you find that you need to go slower, you might wish to bring out your tripod. Think about a remote shutter release, too.
Which metering mode are you using?
If you adhere to matrix or multi-segment metering, your camera will attempt to adequately expose the entire scene. That might not be what you want if you're looking to play with light and shadow. For dramatically lit shots, switch to spot metering and meter from the illuminated area that you wish to be in focus. This will maintain dark shadows while correctly exposing the point-of-focus.
Dial in some exposure compensation
Spot-metering might not be appropriate for your scene, but at the same time, matrix or multi-segmented could render it over-exposed. If that's the case, try dialling in a stop or two of negative exposure compensation.
How are you focusing?
Auto-focus can struggle to hit its mark in low-light situations, in which case manual focus might render better results if you're both confident enough using it and the scene isn't changing so fast that you miss the photo opportunity. Should auto-focus be the better option, ensure that you're using one-shot auto-focus. Try, too, shining a light where you wish your camera to focus. The illumination will assist it in locking-on to the point-of-focus.
Make use of reflection
Whether it's reflection off of pale clothing, off of glass, polished metal, or liquid, or from a reflector, keep an eye out for reflected light and put it to use in your shots. That might be making reflections on water the focus of your photo, but it can also be bouncing back reflected light to illuminate shadows.
Shoot in Raw
If you're not already shooting in Raw, switch now. Not only will help you to tidy up any noise in your shots, or even to adjust the exposure a little if necessary, but it will allow you to adjust the white balance of your photos more effectively. Accurately white balancing low-light shots can be tricky; the more flexibility that you have, the better.
How warm or cool is your light source? Or are you working with mixed light sources? If you're shooting by candle light, you can set the light temperature on your camera to more accurately render colours in your photos. For mixed-light sources, remember to white balance according to the light falling on your subject. If you're shooting in Raw, you might find that adjusting the white balance in post-processing will give you the most accurate result.
Use the darkness
Finally, have fun with the darkness and put it to creative use. Let reflections dance or shadows draw you in to moody scenes. Low-light might force you to think for a moment, but remember that you often have longer than you think you do, and experimenting is half the fun.