When should I start applying to apartments?

I am currently a freshman in college and am planning on moving in with my boyfriend during the summer. We have been dating for 5 years now and feel like we are ready for the next step. I have found four different apartment building in the city and we plan to move into the building in June. Should I start applying in April or May since it is a college town? Also when scoping out the apartments in person are there any little tricks I should look for to make sure it is a good place? Any advice would be amazing. Thank you!!!