I’d start by thinking about what you’re interested in. Nature, mountains, beaches, hiking, wildlife, desert, cities, culture, theatre, food, shopping, theme parks, etc etc.
Honestly the US is quite fascinating, I’ve done a few long drives across it and some of my favourite bits have been the small (or large) towns we stopped in on the way.
Top for me so far have been San Francisco, and Santa Fe.
My American relatives go to the Texas coast, Florida and California.
I’d absolutely recommend doing some long distance driving, and fit in a national park (there are 63 of them so it’s not hard!).