Special considerations like "My mother is elderly and it would be helpful if our room wasn't too far from the lobby", or "We'll be on our Honeymoon and would like a room on the end of a wing if possible for a little more privacy." For our first trip as a family in 2000, my wife asked for a room that faced the pool so she could keep and eye on our older kids swimming while the baby napped in the room (they granted the request).
Whatever you ask for, remember, it's a "request". Don't assume that WDW will give you what you desire. They often will, but it's not a given. We've had good luck, but it's not been 100%. Last trip we asked for a quiet room on the end of a wing. We also gave them the room number of a room we liked last time and asked if we could have it, or one like it again. They gave us a quite room at the end of a wing, but not in the area we desired. We were happy were we stayed. Assume you'll get zero, and be happy when you recieve what you asked for. So many people here assume WDW will grant them their requests and then get bent out of shape when their "wishes" aren't granted.
As, it's suggested that you fax the request in four calendar days before your check-in date. This is the usual time that the room controllers are looking at room assignments for your check-in date.