Added to the above great advice, i'd say try to connect your hobbies/work with people. Most people probably dont have 'close' friends at work, but you can have fun relationships with co-workers. You spend so much time there, have fun with it. Connect with people outside of work, through hobbies or clubs.
I'll repeat what was said above - Exercise and diet are very important to mental health!
Make extra visits to Our Lord and/or do 15 minutes of mental prayer a day. Tell God of your troubles; talk to Him about your day as if He's your friend. Protestants say they have a 'personal relationship with Christ' yet we Catholics forget that we should as well, and even more so because we can recieve Him in communion!