This is just what works for me. Others have their preferred ways.
You need long lengths with tandem axles to keep whatever you're using from sliding apart, plus you can't get much between the wheels.
My preference is (4) treated 2 x 8's cut to 80", 70", 60" and 50" with their ends cut at a 45 angle. Holes drilled through them to line up and drop carriage bolts down through them to keep from sliding. That way you can use from 1 to 4 planks to adjust for height up to 6".
Trouble is that much treated wood adds about 80 lbs weight. So, if that's a problem, go with plastic blocks. You'll need 30 to stack 4 high. A row of 9, 8, 7 and 6. That won't be as high as (4) 2 x 8 planks, but you shouldn't go over 4 high. The other problem with plastic blocks is you'll lose at least an inch as they sink in the ground more than 2 x 8's.
I just got back from a place I had to raise one side 7". Shouldn't have done it. Too dangerous.