When to book is always tricky.
If you plan on eating table service restaurants you must book at least 180 days out. That is a given.
For discounts...that can be a little bit of a grey area, but here are a few bits of info/guide lines.
PIN codes
PIN codes are random. There is no hard fast way to get one, but there are a few tricks that seem to bring results. The first thing to do is to make sure you have an online account with Disney and check all of those boxes that say "do you want us to send you info on X". The second is to plan a sample trip on line that aligns with your travel dates, save it, but don't book it. It has been suggested that this can trigger a PIN code to be sent to you.
General Public Promotions
Many people will suggest that you book what you want early and then wait for a promotion to come out and have it applied to your existing reservation.
This is both good and bad advice.
The good is you can lock up the resort and you want for when you want it. Some of the more popular resorts and room types will be unavailable the closer you get to your travel dates especially during busier times of the year.
The bad is that having a reservation does not guarantee you the ability to simply switch an existing reservation to a promotion. In reality, an existing reservation ever so slightly reduces the chance that a promotion will be offered.
Promotions are offered based on booking rates. If a resort falls short of projections, Disney puts the rooms on sale. If they meet or exceed projections they do not. Having an existing reservation just might be the one reservation that pushes the numbers high enough for Disney to not offer a promotion or exclude that resort from one the do offer.
So what do you do?
Back when I was a Disney TA I would tell my clients to book what they can afford without discounts at least 190 days out. If they were dead set on a particular resort and room type during Holiday season that 190 days could grow considerably, but for your average family, 6-8 months is advance is typically OK. You will then want to keep an eye on discounts and if one comes out you can either pocket the savings at your existing resort or use the savings to up grade to a different resort.
Now that I am a "civilian"
again, I book with the agency I use to work for. (
Kingdom Konsultants). They do all of the discount watching for me and automatically re-book me if a promotion I qualify for comes out. The best part is they don't charge a dime to do it.