There are many factors that influence mental health. Most emotional disorders are created by a combination of "nature" and "nurture"--genetics and environment. When clinicians do assessments, they evaluate the patient's family background and stressors and often make a decision as to whether symptoms have a mostly biological background or are mostly due to environment. Rarely, if ever, is an emotional disorder created only by biology or only by environment. What's most important for the patient to remember, however, is that current environment, behaviors and choices have an impact on mental health. Although the past can't be changed and neither can one's genes, people make many choices in their lives that affect their mental health.
The worst decisions that people make affecting their mental health include decisions to avoid treatment for emotional problems, decisions to continue using drugs or alcohol despite problems with these substances, and decisions to stay in bad relationships. People can also make bad career and financial decisions that often have very negative effects on their mental health later in life (see my previous post http://notesonsanity.blogspot.com/2015/01/do-therapists-give-advice.html.)
But let's reframe this question in a more positive way: What are the good decisions people make that can enhance their mental health?
In addition to promptly seeking help for emotional and behavioral problems, limiting or eliminating substance abuse and other dangerous behaviors and leaving abusive relationships, smaller decisions can have a big impact. Here are some healthy habits:
1. Exercise regularly see my previous post http://notesonsanity.blogspot.com/2014/08/run-for-your-life.html
2. Pursue your dreams while maintaining realism in your career choices (not so easy in practice, which is why it's good to get advice from others whom you trust).
3. Write in a journal. Writing down feelings and thoughts helps people gain a sense of control over their feelings and thoughts.
4. Pursue a hobby. Learning and gaining competence in a field unrelated to your job makes you less dependent on your career for your self esteem and means you can never be bored. Play a musical instrument, take up photography or painting, engage in creative writing, study foreign languages...etc. A hobby can also turn into a second career or at least something to add to your resume.
5. Develop a life philosophy and try to find a group of people who share it. There's a reason why religion continues to be popular despite the Scientific Revolution--people need a sense of meaning, purpose and belonging, in life. But there are many philosophies that don't require belief in a deity or practices that are thousands of years old. These include political philosophies and movements, alternative religions, 12-step programs, and various modern philosophies.
6. Associate with different types of people. Perspectives can become narrow when one only associates with people from one's own socioeconomic class and nationality. Associating with different types of people can lead to insight about expectations and pressures from one's social circle that aren't necessarily helpful but are based on tradition or culture.
7. Become a fan. This may sound like strange advice, as the word "fan" comes from the word "fanatic." But there's been some research indicating sports fans have better overall mental health than people who aren't sports fans, and it stands to reason that other types of fandom may have a similar effect. There is a human need to look to icons, which is another reason why religion survived the Scientific Revolution.
8. Neither ruminate on the past, remain stuck in the present, nor worry excessively about the future. Thinking about the past can be beneficial for two reason: One, to determine a chain of events that led to bad decisions, and two, to reflect on one's accomplishments, which is beneficial for increasing self-esteem. Dwelling on past traumas is not healthy, although talking about them with a therapist might be. People who only exist in the present lose perspective. It's important to remember the past to know who you are, and it's important to visualize and to even fantasize about the future, because this helps you to set goals. Worrying about the future, on the other hand, serves no purpose unless you have legitimate worries that require immediate action.