If you are looking at the NCLEX, then I would say safety and meds are probably the biggest components. Remember to answer as if you have all of the resources you need and time you need, rather than what you would see on a real-life unit.
If you are looking at working in that specialty- the biggest things I always told my students as a clinical instructor was to 1) treat each patient as a person and ask them questions just like you would anyone else 2) be aware of your surroundings and read the room for risk to you or others and 3) learn the key points of your assessments/charting so that you can make it a conversation with the patient rather than a checklist.
If you are looking at certification, I have used Mometrix flash cards and study guides in conjunction with the certification test breakdown. Identify what you know solidly, what you know somewhat, and what you need to review. Keep working through all categories, focusing more on where you need more knowledge.
Know your meds! Almost daunting with meds required/utilized in mental health.
