Important Steps to Mental Health Careers that Require a Bachelor's Degree in Psychology

Developmental
Personality
Clinical
Abnormal
Lab course in Clinical (Child Psychopathology, Measurement, Adult Psychopathology)

Overall GPA.
Psychology GPA minor (if you have one).
GPA last two years in college GPA.
Maintaining a high GPA from your freshman year on
If you do not get an A or B in a course you should probably repeat the course, especially if it was a Psychology course.

Get research experience related to mental health issues to show you are motivated to study mental health issues.
Get even more involved in research by doing a Senior Honors thesis or some other research where you can get your name on a conference presentation or journal publication. This kind of recognition is rare for an undergraduate and will really boost your standing when you apply for a job.
You can get involved in research as part of Independent study course and thus earn credit hours and possibly increase your GPA if it counts as a graded course or volunteer.
An advantage to working in a lab is that you get to know a faculty member who can write you a strong letter of recommendation when you are ready to apply for jobs. Given you need more than one letter of recommendation, it is probably best to work in two different labs as an undergraduate.

By doing an internship you can again show your high level of motivation for a job.
This internship can be with an with an on-campus clinic/organization or off-campus clinic/organization dealing with mental health issues.

There are a number of skills you can develop in addition to what you learn in classes and by conducting research-- computers, writing, and oral communication skills.

You can volunteer at various places that involve mental health issues: a local mental health clinic, mental health wards at hospitals, local, state, or Federal organizations dealing with mental health issues and services.
This involvement demonstrates a high level of motivation and interest in Psychology and mental health. Any involvement just adds to your overall record and makes you a more competitive applicant.

This can include Psi Chi (the National Honor Society In Psychology) or any Psychology club on campus and mental health organizations.
Once again, this involvement demonstrates a high level of motivation and interest in Psychology and in mental health. Any involvement just adds to your overall record and makes you a more competitive applicant.

It is not critical that you are employed in a mental health context (such as those listed above) as an undergraduate, but if you can get such a job that is a real bonus.

It is very important that you start to interact with Professors right away. This can occur by making contributions in class or just going up to your Professors and having a conversation about issues in the field.
These interactions can lead to being able to work in a Professor’s research lab, hearing about job opening that may be available in the Psychology department, and a letter of recommendation.
Remember, if a faculty member does not really know you or had you in one class, there is a lower likelihood that the Professor will agree to write a letter for you or knows you well enough to write a letter.
There are two important things to keep in mind with regard to letters of recommendation. First, a short letter of recommendation from a faculty member who does not know you well can sometimes be worse than no letter at all. Second, It is almost always better to have a letter of recommendation from a full-time Professor than an Instructor. For better or worse, the former simply has higher status than the latter.