This^^^^.
Our trailer always leans a bit to the slide side after deploying it if I level the trailer first. I have found the best was to level it side to side but leave the slide slide one or two marks on the bubble level high. My bubble levels are mounted on the front of the trailer and one one the side. After a while you learn how much to leave the trailer off level before deploying the slide.
I also put down the stabilizer jacks on the slide side after leveling but before deploying it. Even if parked on concrete, the slide side will be a bit low because of springs and settling of the trailer. The reason I put the jacks out before deploying the slide is because the front jack is under the slide and it is very hard to crawl under it and operate the jack.
I only went through this routine if we were going to be parked for any length of time. Never put the jacks down for an overnight or even a couple of nights.
Hope this helps you out a bit. :)
Barney