Definitely contact the professor(s) you would like to work with well before you apply online. Ask them if they are taking students and discuss their future research interests to see if they align with yours. Ask about their mentoring style. It is very rare that people who do not contact professors ahead of time go on to the next round or get admitted. Graduate recruitment weekends fly prospectives out. There is a full day of interviews with professors of your choice, a dinner on the first day. The second day is activities of your choosing (to explore Bloomington) and a party the following day. In the interviews, they will ask about your past research experience and what you want to pursue in the future.