The time of your trip will play a role in the availability. If you’re going at Thanksgiving, the availability will be much lower than if you’re going in early September.
That said, there are lots of popular rides available at 30 days. PP are right that the big headliners are probably not available, but everything else should be. In MK, you probably won’t get PPF or 7DMT, but you should be fine with all three mountains and everything else. At tiered parks, you might not find much for the tier 1, but tier 2 should be there.
That doesn’t mean you won’t get tier 1 FP, though.
As
@Miffy says, there can be better FP availability closer to the date. At 30 days out, people aren’t modifying their plans much, so even if you’re not excited about the selection, don’t despair. Start looking seriously about a week before because 5 days out is the last day to cancel room-only reservation, so you'll see some openings. The night before and day of, you’ll see even more because people will be actively modifying their plans.
It seems counterintuitive that the day you’re in the park would have better availability than a month before, but people often pick up great same-day FP.