LEVEL and FLAT for the surface you are going to unload.
If the camper is downhill, and you pull out from under it, it could collapse forward. It must be level and the jacks must be level.
Having the front a couple inches higher than the rear is an excellent piece of advice.
I never lower my camper right to the ground. I built very heavy duty saw horses the same height as my truck bed. Once I have enough clearance on the rear of the camper, I put the saw horse under and lower the camper to the saw hoses with the jacks holding 50% of the weight and the SH supporting the other 50%.
Then I drive out and immediately put the front SH under the camper.
Once on the SHs it is solid as a rock. And then I can breath again..... :-)