Those students who know what they want are served better. No one should go of they aren't sure. Many students find this to be a good idea. One may have more to show after working in a field related to your major. They look for strong students who know what they want in their field.
Research is valued as well as internships.
Evaluations and strong grades play a major role, also high GRE's help but do not make or break you. Graduate schools use grades as a dividing line, high grades show strong study skills. A GPA of 3.00 is standard. Psychology has a strong liberal arts background and is a good start for other fields. Make sure you take the correct prerequisite for that particiular field.