Therapists suggest making a list of things that are pleasant to you, ranking them in the order that pleases you most, and engage in at least three of them per day. Another useful tool is rational thinking. Depressed people tend to blame themselves for failures and problems, even when they are not at fault. They also tend to over-inflate their problems and minimize their accomplishments. Overcoming irrational thought is the first step to mental health.
Diagnosis is of course the first step to treatment.
At the very end of a chapter on depression, I found something that hit home. It stated that people who seek the support of others who share a common bond or interest are in general healthier mentally. Support groups were credited with helping people come out of those blue funks, and kept others from falling into them in the first place. I had to smile at that passage. After all, I was writing this for L.O.A.D.S. which has been a wonderful source of support to many.