Best to start with a book like this one.
Timing is important, so see: https://www.lonelyplanet.com/north-america/travel-tips-and-articles/when-is-the-best-time-to-visit-us-and-canadas-national-parks/40625c8c-8a11-5710-a052-1479d277f5eb
Here is an interactive map with park ratings, links, and photos.
Look beyond national parks to other federal public lands, state parks, and Native American parks.
You should buy an annual park pass if you're going to visit several parks.
You might want to buy an annual park pass if you're going to visit several parks.