Since Christmas comes but once a year, the rest of the year you have to make do with photographs and memories. The better your photographs, the more those memories will live. Here are some tips for tackling the most common Christmas pictures: CHRISTMAS TREE

Shoot this one the night before, after Santa has arranged all the presents - not after the dawn attack has demolished the fort.

The two best methods require a tripod because of long exposures. Or you can set the camera on a table or hold it against a doorway or other support. One technique is to make a time exposure of the decorated, lighted tree without flash. The room lights should be dim so the tree lights shine brightly. Squinting at the tree will give you an idea of how your picture will look. Adjust the room lights so that, while squinting, you can still see the presents and the ornaments.

Use Type B indoor color film, like Ektachrome B, and expose according to you meter. If you don't have a meter, a good estimate is f-4 at 1 second at either ASA 160 (the professional) or at ASA 125 (the regular). Play safe by making additional frames at f-2 and f-5.6.

Or use daylight film with flash; I prefer this because daylight film makes the lights look warmer and brighter. In this case, the flash - like the room lights in the previous method - illuminates the tree while the long exposure burns in the tree lights. Your f-stop will determine how much light the tree gets; the shutter speed, how bright the tree lights look.

Figure your f-stop by dividing the guide number of the flash and film you're using by the distance from camera to tree. If your distance is 10 feet and the guide number is 65, then the setting should be f-6.3 - or the closest you have to that. For shutter speed, 1/2 to 1 second is about right. Bounce flash off the ceiling and open up two stops from your direct-flash setting for softer, more natural light. OPENING PRESENTS

This calls for quick, press-type shooting: your subjects certainly are not going to pose. Have your camera ready and use flash or strobe. Pre-set your distance and f-stop so you don't have to refocus for each shot; choose a frame-filling distance - about six feet with a normal lens - and move around, following the action, keeping your distance. FAMILY DINNER

Take your picture before the meal, while the table looks its best. Line up your subjects so they're all in focus, asking those on the near side of the table to cross over and stand in back of those on the other side. This also gives a clear view of the table setting. Standing on a chair will give you a better perspective and put the table setting in the same plane of focus as the people.