1. Leave your flash at home and shoot with high ISO instead
Unless you really know what you are doing, I recommend that you not bother using your flashlight. This might come as a surprise to you since most of your Halloween shots will take place in low light situations. However, if you consider how brutal flash lights are when carelessly set, you can probably imagine that not much of the spooky Halloween mood will be left in your photographs. There are experts who know how to do this right although I have yet to see many examples where it was done nicely. This is why I recommend you choose another path: if not much light is available, try to increase the ISO of your camera as much as you can.
When it comes to ISO, you need to know your camera and at which setting it starts to produce image noise to an extent that is unbearable. Once you figure this out, simply stay below this number. Generally, compact cameras with very high resolution tend to show a stronger increase in image noise with increasing ISO numbers. Besides many other things, larger camera systems such as SLRs do a much better job in the ISO department. Keep in mind that each camera has different characteristics. With a few experiments or by studying the EXIF data of the pictures you already took, you can quickly figure out which ISO is useful for you.
2. Use a fast lens
A fast lens is a lens with a large aperture. Such lenses are built to let in large amounts of light into your camera body. How much light your lens is letting in at a time will be a crucial factor when you are out there during Halloween night. The more light, the shorter you can set the exposure time. The best practice is to set your camera to aperture priority mode. This mode allows you to choose the aperture so that you can set it to the largest possible (the smallest f-number). In this mode, the camera automatically chooses the right exposure time for you, which is very convenient.
If you have a little bit of experience, you also know that a large aperture can help you to isolate your subject from the background. This is an important cornerstone for appealing portraits regardless if you shoot at day or night. To give you some numbers, I have successfully been using prime lenses on the streets at night. These lenses had focal lengths between 30mm and 85mm, and maximum apertures between f/1.4 and f/1.8.
3. Shoot RAW
Using the camera’s RAW format over the processed and compressed JPEG format is particularly a good choice when you want to post-process your images. The reason is simply because there is more information in each pixel of a RAW image. In many cases, you might not see this difference when comparing a RAW to its JPEG counterpart with your bare eyes. However, your computer sees much more in these pixels than your eyes. When you process your image, the computer has more material to work with, therefore giving you more freedom when pushing the sliders of your software. The kind of processing I mostly do on nightly Halloween pictures is the use of noise reduction filters and exposure compensation to brighten up the scenes.
4. Move around
Because you won’t use a flash light, you are very dependent on the light that is available. By changing your position and experimenting with angles, you will eventually find light that is good for the sort of images you want to create. Once you find something good, stay there and keep shooting for a while. Take good advantage of the spot you find, but at some point, move on to another one. By changing your position your images will show changing backgrounds. This will not only keep the viewers of your images entertained, but also yourself in the process of taking them.
5. Dress up and become part of the crowd
Here I’m giving you an advice I haven’t followed myself yet. However, I will say that your subjects will look the best and most authentic when you become part of the crowd rather than being perceived as an observer. If you are able to interact naturally with your subjects, they will also appear natural in your photographs. Dress up, be funny, and have fun!