I strongly second that outdoor light exposure (not to mention fresh air) is a great mood boost as well as being pretty essential for boosting your circadian rhythms and keeping synced to day/night. It will help you be more alert when you want to be awake, and sleep easier, more deeply, and with fewer interruptions when you want to be asleep.

N.B. For info about how sleep stuff works + tips and tricks for getting better sleep, check out healthysleep.med.harvard.edu.