A common mistake that beginners will make when attempting astral projection is trying it at night. The best time for anyone to practice astral projection is in the morning. Our melatonin levels are high in the morning and the stress of the day is not weighing down our mind. Also our cortisol levels are beginning to build as our body is preparing for the day to come which helps us stay in an alert mode.
Rather than setting your alarm to wake you up in the morning, try drinking a glass of water at night so that you awake naturally. Once you go back to bed be sure that there is nothing around that will distract you, turn you cell phone off, etc.
The mental preparation may be one of the most important things you can do. It important to not try too hard and let go of any expectations you may have about the experience. Keep your intentions simple at first. You may want to just see if you can leave your body then come straight back and record your experience. Let go of any fear or limiting beliefs you may have through meditation exercises. A good way to do this is visualize the fear or belief leaving your body and entering a purple flame.