Dining is pretty much the only thing you can book ahead, unless you want to do an extra like a tour, for example. If you want to do some kind of specialty dining like a show package or afternoon tea, or if you want to eat at Blue Bayou or Lamplight Lounge, you should book that as soon as your booking opens if you can. Other dining can be booked much closer to the trip, especially if you're not picky about the exact time.
But I wouldn't say it's the only thing you should plan at all. I have seen people who are accustomed to WDW say "everyone told me you don't have to plan for DLR, so I planned nothing" and sometimes those people end up disappointed. For a first trip, I would try to have an idea which few rides you want to do first if you're going to do rope drop, which FP are most likely to run out earlier in the day, understand that character meets are a bit different, know the basic layout, know how to get a decent spot for shows that are important to you, etc. Planning for DLR involves less booking things and more just trying to get a feel for how things work.