When you get those catalogs, check to see what the entrance requirements are. You should determine this information by the beginning of summer so that if you need to take a Subject Test GRE you will have the summer to review for it, then register and take the test in the Fall of your senior year. No later than the summer after your junior year, you should write to specific faculty at each school you are still interested in, to ask about whether they are planning on having space in their lab the year you hope to attend graduate school. A 1-2 page letter describing yourself briefly and positively, showing your interest and knowledge about that professor's particular research, and requesting information on openings in their lab is all that is required. I would suggest writing 5-10 professors this way.
Many students simply choose to go to a particular school without knowing which faculty are there.
So plan ahead and write to the professor and see if they are likable. Once you hear from the Professors, try to arrange an interview at your favorite 2-3 schools. Write to the Department Secretary, and ask for a date when you can talk with the Professor you have written to, and also ask to speak to several other professors in the same general area. It will probably take a month or so to arrange this, so plan ahead to do it early, no later than October of your senior year. Prepare for the interview by getting and looking over some of the papers published by the Professor you like there.