Sometimes bigger IS better – a friend of mine has a 36 foot Foretravel Class A motorhome, and takes great pride in showing me his leveling system. It's a button on the dash. Press the button, and giant hydropneumatic jacks at the four corners of the coach come down and extend until the coach is level. It takes maybe ten seconds. One button. For us campervan folks, it's not that simple. Our rigs can't accommodate the weight and space these leveling systems take up. We have leveling blocks.
For twenty bucks or so, we can buy ten giant Lego-style blocks in a zippered carry bag that we put together to fabricate ramps we drive up onto to compensate for uneven terrain in the spot we camp in. This is more a matter of comfort than necessity, although three way refrigerators need to be within six degrees of level side to side to work properly, because part of the coolant circulation uses gravity. That's side to side of the refrigerator, not of the campervan. The sliding door on some models is also a consideration – more than a degree or two of front to back tilt and it won't stay open or closed. Other than that, level enough is level enough. Unless you have a pet peeve like not being able to sleep if your feet are higher than your head, this isn't something to agonize over.
Modern technology in the form of smartphones and tablets is our friend – all these devices have clinometers (things that measure tilt) in them, that's how they keep flipping the screen around so the top is always up when you turn them. There are plenty of free apps that will turn your device into a leveling display – I like one that displays a bubble level. When I drive up a camping spot, out comes the tablet and down on the floor in the aisle it goes. In addition to the bubble, it also has a readout in degrees, which will tell you how tall of a stack of blocks you need to get level.
Because our campervans are roughly twice as long as they are wide, blocking up one side will raise the van twice as much as blocking up one end. Therefore, if you have a choice, it's better to park the van so the tilt is side to side rather than front to back – it'll only take half as many blocks to get level. The math is simple, too. One layer of the orange blocks front and back will raise the van enough to tilt it one degree side to side. Two layers will tilt it one degree front to back, roughly. It depends on the wheelbase. My long Sprinter with its 170 inch wheelbase is pretty much impossible to level front to back unless it's only a degree or so off. Here's a massive six block stack, which reduced the five degree tilt of this camping space to two degrees. Of you're short on blocks, you don't have to complete one side of the pyramid, provided you remember not to drive off the incomplete side.
If you have more storage space than I have, you may consider the ramps Class Cs use. Be careful with the curved ones, though, because if you overshoot they can damage the water tank and its fittings behind the right front wheel. Driving off the front of these curved ramps will force them up into your undercarriage, a fragile area on many campervans.
If you have dual rear wheels, remember that the weight of the van was designed to be supported by both wheels, not just one. Even sitting still, stick to the recommended weight limits for tires. It's OK to cheat a little by making only one ramp, with a stack of blocks of equal height for the other wheel. You only need one ramp to get up, and the stack will allow the weight to be distributed to both wheels once you are up.