Is there anything I can do to prevent getting psoriasis?

No. Psoriasis is an inflammatory disorder that is inherited, although sporatic cases also occur. There is no way of preventing psoriasis from developing. The onset is generally in adulthood, although a small subset begin in childhood. This is a systemic disease that involves the skin, nails, joints, and we're now learning that it also affects the cardiovascular system.
Not necessarily . It is an inherited and genetically based immunologic disease -- it can be precipitated by stress or infections though.