I have two answers; A friend said you should always level your bed and hope the rest is close. That way you are less inclined to fall out of bed after a long night. A mechanic told me to always level it so the fridge is as close to level as possible. The fridge is most sensitive to being off-level, so it should come first. Of the two, I'll buy what the mechanic said. Fortunately, when my fridge is level, since my trailer is well formed, everything else is also level.
With every trailer I have owned, I first take it to a very flat, level place, level it to as close to ideal as I can make it, then install a set of Hoppy's Levelers. I then re-check it annually. Using them I can usually get within 1/4" side-to-side, then entirely level front-to-back.