You can make room requests, which are not guaranteed, by calling MS (or sending an email in the contact section in the member website).There is also a room request page when you check-in on line at 60 days before your arrival. However, that page was designed for regular Disney cash paying guests, has more limited requests than can be made via MS, usually has some requests that are pointless for
DVC rooms (e.g., high floor for AKV Jambo when all the DVC rooms are on the fifth floor except for club level on the sixth). Thus, it is better to make requests through MS and skip that online page -- actual use of that page wipes out any prior requests made through MS.
As to kinds of requests to make, the broader the request the greater the chance it will be met, e.g., requesting a general area for location is more likely to be met than requesting some specific room numbers. Also, be aware that if a location request cannot be met, they do not bother to try to find for you something close to the location you requested, but instead go immediately to placing you anywhere that is open; for example, a close to lobby request at AKV Kidani, if it cannot be met, could result in your ending up as far from the lobby as you can possibly get (in fact, many have reported that result which places you about 1/3 mile from the lobby at Kidani). Thus, again, you should usually try to make any location requests as broad as possible to both increase the chances to get it and avoid ending up in the outback. Finally, you can make multiple requests, e.g., high floor and close to lobby, and if you do so they will try to meet them in order given. Thus, choose order carefully; in my example, if principal desire is close to lobby rather than high floor, then make sure you give close to lobby as your lead request.