Timing is everything. Knowing when the moon rises and sets helps you decide when you want to go out and take pictures, or what effect you'll get on any given day. Similarly, knowing with twilight occurs can also help you time your shots to achieve a certain look.
The US Naval Observatory has an online tool which produces a one year table of sun or moon rise and set times. All you need to do is enter in the coordinates of your location and it'll do all the math. I used to use this extensively, but looking up the coordinates for a location and typing them in is a bit of a pain.
After getting tried of struggling with coordinates, I created Sun or Moon Rise/Set Table for One Year a simplified interface to the US Naval Observatory's tool. Instead of manually keying in coordinates you can now pick your location from a map. Easy!
Now you can plan ahead by looking at the astronomical conditions and you can schedule your time accordingly to get the effect you want.
When taking pictures at night a flashlight is extraordinarily useful. You can use a flashlight to: light up the dials on your camera so you can change settings, light up your subject so you can focus the camera, do some light painting while you take the picture, and keep yourself from tripping over things in the dark.
What type of flashlight you bring is a matter of personal preference. I prefer a headlamp since it frees up my hands; however other people prefer large Maglites for the feeling of security that a large heavy flashlight can provide. I recommend looking for flashlight which is compatible with common battery sizes, can take coloured filters, has reasonable waterproofing, and is easily repairable.
If you are looking to take some clear shots of the stars in the night sky, the best time to try is in the winter or on cold nights.
One element that distorts pictures of the sky is moisture. While this at it's most dramatic this moisture takes the form of clouds, there is some degree of moisture in the sky all the time. The capability of the air to hold moisture is dependent on temperature, so warm air holds more moisture than cold air.
The clearest pictures are available on the coldest nights since the air lacks the capacity to hold much moisture, so starlight passes through the atmosphere with very little distortion when it is cold out.
What happens when you take a picture with an SLR? The mirror of your camera flips up, the aperture closes and the shutter opens. This is all a lot of activity and movement happening immediately prior to the exposure, and in some cases the residual vibrations from this can cause some blurring in your pictures.
In most cameras you can reduce the vibration and increase the clarity of your pictures by enabling mirror lock-up on your camera. Mirror lock-up moves the mirror of the camera out of the way long enough before the exposure begins that the vibrations can subside. This setting can be difficult it is often buried away in camera menus, but mirror lock-up can be a valuable tool to coax a bit of extra clarity from your camera.
Ever had a roll of low sensitivity film (eg. ISO 200) and wish it was more sensitive (eg. ISO 800)?
Push processing allows you to increase the sensitivity of film by telling your camera that you are using a faster speed of film than you are, then developing the film at the new speed rating. This has the effect of underexposing the film in the camera and then overdeveloping it, so the overall effect is a properly exposed picture. This allows you to take pictures in darker environments without sacrificing your other camera settings, but it does cause higher contrast, increased grain and lower resolution.
To push film; set your camera to a film speed one or two stops faster than the film you are using and take pictures normally. then lengthen the development time to compensate. Some cameras detect the film speed automatically, in which case you would want to underexpose all the pictures by one or two stops to get this effect.
Where I live the temperature frequently drops far below freezing in the winter, so holding onto a metal tripod for any length of time results in numb hands. One way to increase the comfort of your tripod is by insulating it.
Attaching pipe insulation to the legs of your tripod is a cheap way to improve your tripod since it not only keeps your hands warm in cold weather, but it also adds some padding so you can carry your tripod over your shoulder.