It depends on how your school conducts OCI (on-campus interviews). There is no formal application process for most, at least to get the initial interview. Generally the higher ranked schools award interviews w/ firms on a bidding system. E.g., 14 interview slots for firm X. You rank firm X as your 5th choice, but 18 ppl ranked it as their first so you will not receive an interview. Moreover, four of those that ranked it number one won't receive an interview.
Other schools, generally the lower-ranked schools, will have you submit your materials (resume, cover letter, transcript, and writing piece). Then the firm recruiter will invite you to an interview.
Whichever way your school conducts OCI, you will want to get interviews for firms that have a strong practice in that specialty. Recruiters will ask you if you know what kind of law you want to practice. You could always tell them, but you might want to leave it a little broad in case they don't currently have enough work to justify hiring someone in that dept.
In the long run, you could always switch over to a particular specialty w/in a firm or lateral out.