Summarize:

If you are staying awake longer than normal, you'll have to resist the temptation to sleep. Stay out of bed, don't wear pajamas, and avoid anything else that is part of your sleep routine. Keep the temperature warm enough or cool enough that you are slightly uncomfortable, and more likely to stay awake. Your body's basic sleep cycle is tied to light during the day and dark at night. This means that dim lights can make you sleepy, especially if you are staying up beyond your usual bed time. Bright lights, however, can increase alertness. Keep lamps and other sources of light on when you are trying to stay awake. Staying awake in company can be easier than trying to do it alone. Talking, studying, listening to music, and taking breaks with others can be stimulating and help the time pass by. An alarm clock can be a good back-up when you are trying to stay awake, especially if you have to do it alone. Try setting an alarm (or several) for regular intervals, such as every half-hour. That way, if you accidentally fall asleep, it won't be for very long. If you are staying awake while getting work or chores done, try switching tasks every now and then. The change will provide some mental stimulation, especially if you move locations (from room to room, or from indoors to outdoors, for instance).
Don't get too comfortable. Keep your environment well-lit. Keep company. Set alarms. Mix up your activities.