Environment is important to keep yourself asleep. Good sleeping hygiene and maintaining the perfect sleeping environment, while not necessary, could keep you comfortable through the night. This not only helps you sleep but also keep you asleep. Then make sure everything stays consistent through the nights. Lights leaking through the curtain from windows when a car drives pass your room could be a problem. Even the alarm clock or phone beside your bed, just turn it around away from you.
Noises too should be minimized. You can’t really avoid the occasional ambulance, but you can try to reduce it. Get some white noise in your room, a soft consistent noise should help you remain asleep (e.g. leaving a fan on). The noise should have a minimal amount of volume and pitch variation. Or just give ear plugs a try. Practice a sleeping habit. No huge meal, no exercising, no alcohol, no heavy activity before you go to sleep. Avoid taking naps just so you feel more tired at night. Once you get into a good routine, the body might feel better as well and take comfort in staying asleep. There you have it. The key to staying asleep might be to keep yourself sleeping at ease.