How do I level my trailer?

You don't need it exactly level unless the trailer has a working propane fridge. Otherwise, get it eyeball level and then place your jacks at 4 points. Walk into the trailer to be sure it's reasonably level feeling and the pillow end of the bed is not on the low side. LOL. The jacks should be snug enough to make the trailer feel solid.

It can be fun if the spot you are setting up on is out of level but here is what I do with the Lil Loafer:

1) Position the trailer where You want it leaving it connected to the truck.
2) Look at the back end of the trailer to see if one side is low and needs to come up to make it level.
3) Roll the low side onto a wood block to get it reasonably close to level; use a short spirit level if you don't have an eye for level. (I try to have the head end of the bed side slightly higher).
4) Place two wheel chocks on both wheels to be sure it won't roll and disconnect from the truck.
5) Lower the coupler end to raise the back end.
6) Position the jack stands on the back end under the frame; assuming you are using conventional stands.
7) Raise the coupler end until looking at the side it is reasonably level, use the spirit level if that helps.
8) Position the jack stands under the frame at the front.
9) Lower the coupler until the trailer is fully supported on the jack stands and give the trailer a little shake and rattle to be sure the jack stands are fairly solid.
10) Crank the trailer jack back down so it contacts the ground just enough to share the load with the front jack stands.

Removal is basically reversed.

I like to keep a seven point contact; 4 jacks, 2 tires, and the trailer jack.

I'm level when my wife tells me I'm level. If she says the bulls eye level is off...she's right!

With that said, the suggestion of bringing blocks of wood is a good one. We've all had the impossible nobody-wants-it site. A couple of foot long pieces of 2x8 can save the day.