I am currently a student studying to become a clinical psychologist. Some of the undergraduate classes you will take include introduction classes (i.e. Introduction to Psychology), core courses (Introduction to Psychological Research, Social Psychology, Developmental Psychology, Biological Psychology, and Cognitive Processes), and psychology electives (i.e. abnormal psychology, personality, research under faculty, community applied psychology, etc.) To complete your undergraduate degree, you will also need to take 2-3 science and 2-3 math courses. I would recommend taking statistics as one of your math classes since it is extremely helpful when trying to understand some vocabulary in Intro to Psychological Research. Biology, Anatomy and Physiology are also good science courses to take that will give you a good understanding of the human body and prepare you for biological psychology. English and other humanities courses will be required as well and will help you develop better writing skills.
If you are up for it, learning the R programming language would be useful as if research is in your interest, you will need to know it. Once you have finished your undergraduate degree, you will need to apply to graduate school. This can be done at any time as experience can be extremely important. Getting an internship for a year or two will only help you. When applying to graduate schools, make sure they are APA credited, so you can obtain certification. Applications include transcripts, letters of recommendations, resumes, personal statements, and test scores (GRE is the most common, but MAT is accepted in some schools). Be aware that many schools look at everything, so having one bad things can be outweighed by having strong scores in everything else. Once you submit your application and get your acceptances, celebrate(!) and then evaluate what school is best for you. Remember, don't compare yourself to other people's accomplishments. Getting into any graduate school is amazing, so good job! Once you are in graduate school, your classes will be more focused on clinical psychology and getting hours of practice in.
Once you have obtained all your graduate credits (either Masters (2-3 years) or PhD (5-6)), you will take an exam to gain licensure to practice clinical psychology. There are books to study for both GRE or MAT and licensure exams. Buying and studying those will be useful, so you can get the best scores possible. After you have gained licensure, you can either join a company as a clinical psychology or even start your own! Depending on what you want, it's all your choice from that point on. Hopefully, this is helpful!
I went to school so long ago (I graduated with my Ph.D. in 1972) that my experiences are probably out of date. If you decide to major in psychology the department will have a list of required courses, plus suggested electives. In my opinion some background in statistics and biology is helpful. I also suggest you take some literature courses that require writing; there is a lot of good psychology in well written novels, plus many employers today want employees who can write and express themselves well.
I recommend you look at the web sites of some colleges in your area and see what the requirements are for a major in psychology. Most colleges are happy to talk to prospective students.
Good luck with your career pursuits.
Ray Finn, Ph.D.