Please keep in mind that Disney uses almost all of their rooms, so some people will have to stay in rooms with less than perfect views, and no room requests are ever guaranteed. Remember, also, that you probably won't spend much time enjoying the view, but instead you'll spend time enjoying the resort and the parks. So, in cases where you don't get the perfect view, try to not let it spoil your vacation.
Nevertheless, there are ways to improve your chances of getting a better view. The first thing you can do is pay for a room with a specific view. Many of the resorts allow you to pay a small premium for better views (garden, water, etc.). If you only pay for a standard view room, you are more likely to be disappointed with the view (parking lot, another building, etc.) than if you pay for a premium view.
Secondly, decide what are your one or two key , and ask your travel agent (or Disney) to add those preferences to your reservation. Try not to ask for too many things, as it might be confusing for the folks assigning your room. For example I recently added a preference for "close to the lobby" and "non-parking lot view" to a room reservation.
Third, if you are still concerned, you can call Disney 4-10 days before you arrive and ask for "room assignments" or "back office." If all goes well, you should be connected with the room assigner at your resort, so you can discuss and clarify your request. I was given this tip by several managers of some of the Disney resorts -- they told me to share this tip, since they also want to work with guests in advance to help make the right choices. Once you arrive for check-in, it is often very difficult to make corrections, as all the other rooms are already filled.
Hope that helps. If you want further details you might also want to read THIS prior Q&A.