Whenever someone feels depressed, the first thing is to do something outwardly to make him happy.
Like if he doesn't have money or is not working then let him find a job.
At this point in life, philosophy doesn't work.
Anyone can be happy if he has proper bread and butter.
But still, ways to keep oneself happy might include, pursuing a passion in life, having good health and good relations. Other factors may be like enjoying small things in life but obviously, if they are without any addictions of drinking, partying, caffeine and drugs then only they work fully.
Addictions will give you short term happiness, not internal full-term bliss.
What do you think are the ways to be happy?