What are causes of waking at night & how do you prevent them?

Poor sleep hygiene. Avoid things that disrupt sleep patterns, such as alchohol, nicotine, caffeine, excess exercise or eating too close bedtime. Promote better sleep cycles sleep by darkening the room, and retiring at the same time each evening. You might also consider earplugs if your environment is noisy. It is also possible that you have sleep apnea that can disrupt your sleep. Discuss this with your md.
Sleep apnea. I find that most of my patients that wake at night unknown to them have sleep apnea. Although you don't hear yourself snoring, it may be waking you up as you gasp for air when the airways get blocked. Talk to your pcp about perhaps getting a sleep study.