With so many new campers on the roads this summer, I continue to hear this question, and continue to see people struggle at the campgrounds. While I am using Lynx Levers and X chocks, you can do the same thing (and we have for years) with 2x6 wood planks and plastic or rubber chocks if you're starting out (but the chocks and the levers are worth the small investment in convenience and performance). This isn't the only way to do it, by far, but its a great starting point and includes stuff I've picked up over the years. Hope this helps!
Lynx levers:
https://www.amazon.com/TriLynx00015...

X chocks:
https://www.amazon.com/XChockWheel...

2/4 way bubble level:
https://www.amazon.com/HopkinsTowing...

1 way stick on level:
https://www.amazon.com/Camco25503Ut...