When professional mental health clinicians are asked to figure out what is wrong with a patient, they assess that patient broadly, using something they call the "bio-psycho-social" model as a guide. The bio-psycho-social model assumes that mental health problems are hardly ever limited to just one domain of human experience (say, just a "mental" problem). Instead, most mental health problems are influenced by multiple domains of human experience, and have biological (medical), psychological (mental) and social/spiritual impacts. For instance, someone who is depressed, might have become that way because of a medical condition (such as a heart attack), a social condition (such as losing a loved one), or a psychological condition (such as an overly self-critical nature). Further, regardless of the cause of the condition, that person's depression will likely show physical symptoms (such as slowed speech and lessened appetite), psychological symptoms (such as suicidal thoughts) and social symptoms (such as social withdrawal). Perhaps most importantly, it is possible to treat depression through physical means (anti-depressant medicine, physical exercise), psychological means (cognitive therapy) and also social means (urging the person to get out and interact with other people) regardless of how that depression got started. All of these methods are likely to prove helpful in lifting depressed mood. What is more, they can all be used at once despite their different origins; you aren't limited to trying one intervention at a time.
The idea of being broad in your assessment of the nature of your problems remains a good one, even when your problems ultimately turn out to be simple ones and the full bio-psycho-social model doesn't really apply. It is always a good idea to keep in mind that your problems will sometimes be more complicated than you initially thought and require you to try a variety of solutions before you are able to make any headway with them. It is also a good idea to keep in mind that you might benefit from using more than one self-help method at a time, and that such methods might address seemingly very different aspects of your experience and still be effective.
Mental health professionals' use of the bio-psycho-social model reflects their understanding that human beings are biological, psychological and social creatures all at the same time. People seeking to benefit from scientific wisdom for purposes of helping themselves better manage life problem are wise to copy this comprehensive professional approach and do what they can to learn about these three important aspects of human experience. A basic understanding of medicine and human biology theory helps people to understand how their bodies and brains are constructed and then affected by disease. A little background in psychological theory helps people to understand how minds develop and operate, how thoughts and feelings work, and how behaviors and attitudes can be changed. Finally, knowledge about how relationships and other social processes (gained from learning a little about sociology and social work theories) helps people to develop an appreciation for the social systems in which people live and the impact these systems have on their group and individual health.
It can feel overwhelming to think about needing to learn about medicine, psychology and social sciences all at once! And yet, all of these fields are important in their own right with regard to informing self-help. None of them can be sacrificed or set aside in favor of another if you are to understand a balanced picture of how human problems occur and can best be fixed. Fortunately, it is not necessary to become an expert in any one of these fields to benefit from them. Learning certain basic ideas and observations which are fundamental to these fields is all that is needed. Learning these basic ideas will help you to determine when problems are serious and require professional help, and when they aren't serious and can probably be handled well on your own. They can help you to know what general directions to go in; what basic steps to take to successfully handle different types of problems.
Before discussing the various ideas and theories, we want to point out a non-obvious truth. Just because a theory or method we describe here is "scientifically based", doesn't mean that it will be able to offer you a good and accurate fit for your issues. Scientifically supported ideas and theories are developed based on systematic group observations. The solutions and concepts they offer accurately describing group behavior (at least for whatever groups were studied), but they are not always a good fit to any given individual. You need to use your judgment, and the judgment of others whose opinions you value (because they are wise) to help you determine what fits you and what does not. If a theory or method doesn't make sense then don't choose it.