Getting the work/life balance right is crucial and finding time to exercise during the week, not just weekends can be important in getting this right. Join a gym or club and find a night of the week to commit to. Going with a friend can make this commitment harder to break at the last minute. Make sure you have some interests outside of school or just get involved in something.
Since making sure I have some school free time I have become much happier and enjoy my work much more than I did before.