Leveling

Within the the center buble is good.
If your leveling system has indicators, use a 24 inch contractor style level on the galley counter top to see how close the leveler indicators are. Adjust the levelers control so it is accurate.
Leveling blocks are not normally used in our case. We carry a set of blocks. We also carry four 12+ inch square plywood pads to go under the levelers. They are used in soft soil to spread out the weight.
I haven't used the plastic Legos in several trips. Considering leaving them at home. Then I will need them.
Definitely keep the rear wheels on the ground. My rig has parking brake on drive shaft. On uneven ground lifting too much weight will cause the rig to roll off the kick down jacks.

it really depends on how far that bubble is off dead the center.
i try to have it level as as can because i find it a bit irrating to fight the force of gravity on while sleeping on a slope. at the least, i try to park it so that where i rest my head is higher than where my feet.

mockturtle wrote:
If I have half a bubble, I'm satisfied.

X 2

If I have half a bubble, I'm satisfied.

I'll get fairly level (so the bubble it at least 50% inside the target bulls-eye. That way the sink & shower drain properly and the dear wife is happy cooking. (and THAT is important, I kid you not)

If getting level means I need to cause a tire to lose contact with the ground, then I retract the jacks and put either 2" or 4" of 12" x 24" planks under the wheel (back up and drive on to the plank) then level again. If 4" of planks won't do it, then the site doesn't work for me. (Very rarely happens)

I echo Mandalay - ALWAYS keep your rear wheels in solid contact with the ground.

I only get mine reasonably level. Doesn't have to be perfect.
I just get it so the bathroom door doesn't swing. Only need blocks if you sink into the ground.
NEVER get the back wheels off the ground. That is where your parking brakes are.