Now that '
Free Dining' has been announced, if you are going in that time period you should call immediately!
If you are staying on property, you can make your ADR (Advanced Dining Reservations) 180 days from your date of arrival and for the next 10 days (if you are staying that long). You'll see mentioned here on the DIS 180+10. It's not 190 days it's 180 days from your arrival and up to 10 days of your stay.
You should have an idea of where you want to eat and on which days and times. Be flexible because Restaurant A may not be available on day 1 but might be on day 4. Get the idea?
Also, depending on you party size there may not be any availability. So, if you are a party of 5 or 6 and there is no availability and you can split your party into two sets you may get your ADR.
A lot of this will depend on when you will be at WDW.
The more prepared you are for the call the better it will go.
If you must eat at a specific restaurant, then rank your choices and start with the 'must do' restaurant first so you can check all the dates of your stay.
Keep in mind if you are wanting to see one of the parades/shows so you don't schedule your reservations at a time that will not permit you enough time to get to the parade/show. At Epcot, some restaurants are favored at certain times b/c of the ability to see Illuminations while dining. Gotta know all this stuff if it is important to your experience.
I know, I know, lots to know to make a darn ADR. But, the more prepared you are the better you call will go. Plan on sufficient time if you are making lots of ressies.
Best Wishes!