I have been studying psychology for 6 years. I started in high school taking 2 years of International Baccalaureate Psychology. After that, I majored in psychology for my Bachelor's degree and took many more classes than I needed to graduate. Throughout these 6 years, I've learned many study skills that helped me achieve a 4.0 GPA for my major. I also noticed many of the maladaptive study habits that other students tried and that kept them from being successful.
The best advice I have for succeeding in psychology is to start everything early. For me, this meant changing the due dates in my calendar to earlier than the due dates set by the teacher. For example, if a paper was due on November 30th, my calendar said that it was due on November 20th. This was my goal for completion. I also set sub-goals for myself to prevent procrastination. For a 10-page research paper, my calendar would have "due dates" for literature review, creating a list of references, writing an outline, and writing the first 3 pages. I spread my work out throughout the quarter so that I would have less stress and more time to resolve problems that came up. This method works like a charm. During my last quarter of undergraduate school, I had to write 4 research papers in 10 weeks, in addition to all the other course requirements. I finished all of them on time and received A's on each.
In studying for tests, avoiding procrastination is also key. Don't wait until the week before the midterm to attend office hours. Do the reading each week and make flashcards immediately after reading the chapter. Create a study group to talk out main concepts that you don't understand. The week before the test should be mostly about review and solidifying terms into your memory. The actual learning should occur throughout the quarter.
Lastly, be kind to yourself if you are struggling. Psychology is a VERY hard subject. If you make some changes to your study habits and receive help from a tutor, you are well on your way to receiving an A!