It's not clear how long it has been since you have graduated with your bachelors degree. IF it's been more than 10 years AND you have not kept up with recent research in the field, be prepared for the need to take remedial coursework (i..e, upper division undergraduate courses) in order to come up to speed - some of what you learned may be obsolete...
The amount of effort that you will expend in studying will be significantly more than what you expended as an undergraduate student. Professors will expect a lot more independence from you, i.e., no hand holding. Get involved in the research program of one of the faculty members. In fact, you should select a graduate program on the basis of your research interests and the faculty members doing that research.