How do you level?

i first look at my site or the spot where i'd like my trailer, look at the terrain for which side will be high or low...i back in where i'd like the rig set. I carry a 4 foot level with me and i place that on the floor in the trailer from side to side...over time, you can tell how much correction you need to make level. i also check at the a-frame right by the front wall as well as in the rear. once i figure what is needed, i pull my rig forward a few feet, get my levels out and stack them up. i have a slide out, so i keep that in mind and compensate for it. i've never been on a site that i've had to use more than probably 3 courses of levelers high. once i'm done my trailer is always inside the lines on the level usually about as level as can be.