Basically during block 7 they will come talk to you about this, but the way it works is you'll get a presentation on available sites and their rotations, then you'll have 2 weeks or so to make your decision. They will give you a piece of paper, where you have to rank all core locations (and some, like NRV / Roanoke, will have core sites that you have to rank within them). The paper also gives you a little space to state your reasons for your top location and site choices. This is where you would put in the location of your significant other, previous work experience with the hospital system, etc. You will also get a second sheet of paper where you can claim special circumstances (Children in school or with special needs, or family members with special needs, or if you are married to another VCOM student, requesting placement together). If you claim a special circumstance, they will require documentation proving it (i.e. school enrollment proof, physician letter, etc).
Once they get everyone's paperwork, they'll start to work on core sites. If there are fewer requests for a site than there are spaces, then everyone gets a spot. If there are more requests then spots, then individuals with special circumstances get priority, and everyone else goes into a random lottery to see who gets the leftover spots, and who has to go to their 2nd or 3rd choice rotations. So the chances of getting your prime location are dependent on both the popularity as well as the number of spots available. I think unofficially, people who are married/engaged to non-VCOM students with good jobs get a little leg up as well, but they won't confirm that. Long-term girlfriend/boyfriend, however, may not help you out.
A few weeks after turning in your selection forms, they'll send out the core rotation assignments so you at least know where you will be, and you can start looking for housing. You won't get your rotation schedule until later.
Overall, I think they do a pretty good job with it. Sure there are some people that are unhappy, but for the most part it's as reasonable of a process as can be.
Hope this helps.