1) get to know the various types & options. Generally, for self-propelled, there's class A, class B & class C. Towable RV types include toy haulers, pop-ups, etc. See below for definitions.
2) Rent one to get a feel for what's it's like. Many campsites (KOA, Jellystone, etc.) also rent cabins, so you can go camping even if you don't have an RV, so you may not need to buy an RV at all. Just load up your van with your stuff & stay at a cabin. This is what we do. It's very cost effective, since you don't have to shell out money for the gas, maintenance & other expenses of owning an RV. Many camp sites also welcome tent camping.
I like class C motor homes because they are economical, full featured and easy to operate & maintain. I don't like slideouts because they are more expense, and complexity. They also can leak.
General info:
https://www.generalrv.com/blog/rving-101-rv-types/
RV rentals (they also sell used RVs):
https://www.cruiseamerica.com/