Also
Register on the disneyworld.disney.go.com/plan/ website. Do it soon. Then set reminders on your calendar to book your FastPass Plus rides and your restaurant bookings. And download the My Disney Experience app. The parks now have free wifi so you can use this whilst there too.
Are you staying on site? This makes a difference as to how far in advance you can book things? See below...
Have you bought your theme park tickets yet? When you have you cn link them to your Disney Experience account. Sooner you get them, sooner you can start booking FP+
FastPass Plus
If you have park tickets, you can choose FastPass+ experiences up to 30 days in advance. If you have a Disney Resort hotel stay, you can make selections up to 60 days prior to check-in.
Advanced Restaurant Reservationss
You may make a dining reservation at most Disney World restaurants up to 180 days in advance of your meal there.
It is worth reading their planning pages, or using a website such as The Dibb for more information.
In school holidays it really is necessary to use FP+ for popular rides, and to use ADR. This is especially the case for character meals, but also for a lot of the other restaurants. There are also other outlets in the parks where you can take away or just turn up, though these tend to be more burger/fast food joints.
It means planning your days ahead of going, and not having as much flexibility as you may normally have on holiday. However, FP+ don't have to be used and you can also add another one when you are there - after you have used your first one (do it as a FP booth or online.) Likewise, you can cancel resturant bookings up to 24 hours before with no financial loss, and can make more when there though you will be more limited to which restaurants and/or times available.