Read up on all the mental illnesses in your hesi book and know the signs of each one.
Know the proper medication for all the mental illnesses in your hesi book.Know what time of day they should be given, labs that need to be monitored, dietary restrictions and pertinent side effects like decrease in libido.
Be aware of extrapyramidal side effects and neuroleptic malignant syndrome. Know the characteristics of each and treatments if any.
Practice a lot of mental health questions. Learn how to apply therapeutic communication and how to provide care to patients gradually.
Study depression carefully and be aware of how to care for the suicidal client. know how to respond to a client with a plan to harm himslef and how to get this information from the client.