In addition, ask other graduate students about what it's like to be in their doctoral program - both good and bad experiences. Ask them specific questions about their program and it's requirements and what the lifestyle of a typical graduate student is like. You should also talk to professors who know you well and ask them whether they think you have the potential to succeed as a graduate student. For information about other universities, look at departmental webpages and find out what the degree requirements, faculty research interests, etc. are for their program. These questions were adapted from UCSC's Psychology Department's Field Study Program website.
Psychology graduate school admissions departments look for in applicants.