AP discounts act like other Disney discounts....they come out at various times of the year, cover certain dates, vary by season, and vary by resort. AP discounts tend to be roughly 5-10% better than the general public discount out at any given time, although that's not always a hard/fast rule.
AP discounts often (but not always) come out
after general public and other types of discounts, but they have longer "book by" windows than other discount types. Disney's standard "the number of rooms allocated for this offer is limited" disclaimer is very much in effect.
Availability can be limited for certain resorts/room types/dates, so you have to pay pretty close attention to when things are released and be somewhat quick on the draw, if the discount is critical to you.
Using last year as a guide for your particular circumstances...
General public discounts (10-20% off rack rate) that covered early December were released 8/8/2016
AP discounts (20-30% off rack rate) that covered early December were released 8/23/2016
This is a handy website to bookmark to reference these kinds of things:
https://www.mousesavers.com/historical-information-on-walt-disney-world-resort-discounts/#2016
Often when I have a specific resort/room type/set of dates in mind I'll make a rack rate room only reservation, then watch the general public discounts when they come out and apply it if available, then watch the AP rates and apply that discount when/if available. It is VERY easy to change/add discounts to room-only reservations online, you don't need to call. If no discounts ultimately come out then I make a decision if I'm ok paying rack rate where I originally wanted to be. Although like I said, I tend to do this when I have a specific trip/dates in mind and am not likely to cancel.
There will be people that

at what I just described because they say Disney will offer less discounted inventory if they have high rack-rate bookings, but I don't so much buy into this line of thinking. Disney knows exactly what they are doing to meet the market to fill rooms.
If I don't really need to peg a resort/room type/dates, I won't make any reservations and will just wait until later when discounts do come out to make booking decisions.
Sorry, long post, but hope that helps/makes sense!