Unit 4 psych is comparatively more straightforward (imo) than Unit 3. I think for unit 4, put extra special focus into your operant/classical conditioning principles and learn to distinguish between and identify UCS/UCR/CS/CR in Classical conditioning scenarios and the 2 types of reinforcement and punishment in Operant conditioning - there's always a question about this on most past exams
Also, I found schedules of reinforcement (fixed ratio bla bla) to be sooo annoying haha so probably learn to distinguish them correctly and how they can be applied in different situations (see last year's exam - there was a whole Q on it!). Also, try to learn most concepts like stress/phobia (as well as your detailed study) in terms of the biopsychosocial framework (i.e. biological, psychological and social factors which influence these conditions)