- Wrong temperature
Though it is much more pleasant to fall asleep in the warmth, the optimal temperature for sleeping is 15–23 °C. 
- Physical activity
Physical exercises excite the nervous system, so after class at the gym, it's difficult to fall asleep
- Absence of a regime
Fall asleep at the same time - from 22:00 to 01:00.
- Lighting
Every light can prevent a good sleep. Get rid of all light sources or use a mask for sleep
- Caffeine
Caffeine is found not only in coffee, but also in tea, chocolate and some other products. Decrease in the afternoon consumption of food, which include caffeine. 
- Alcohol
Though alcohol helps you to fall asleep faster, it negatively affects the phase of fast sleep. Use alcohol not late than 2 hours before sleeping. 
- Wrong body position
Scientists have established that the ideal position for a comfortable sleep, which, in addition, stimulates digestion - on the left side.