I know everyone has given their method of leveling their trailer. So.... Here is mine. This doesn't mean I am right and others are wrong. It is just my method, which I think is easy and works.
As you said you level side to side with boards. That is good. I used boards and I used the lego blocks. So far you do the same as I would. I have a set of orange pads that are about a foot square. I would place one of them on the ground where my landing gear would go. This would keep your landing gear from sinking into the ground if it is soft. Lower the main gear a few inches. This will give you room to drop the nose if necessary to level the trailer. Once this is done, pull the pin on the leg extensions. This is the ones inside the legs that has all the holes in it. Each one should be lowered to the ground. Depending on the side to side distance needed to level the trailer side to side one will probably descend further than the other. This is OK.. When you put the pin through the leg, what Jimtoo suggested is correct. Make sure the pin goes all the way through the leg. You should feel it on the inside. If not, find out why, because you will bend the tip of the pin if you don't. If one foot is just a little bit off the ground when the pin is inserted, you can do either of two things. Find a board with a thickness of the distance and set it down on it. Or you can raise or lower the legs just enough to get the pin in. You want to raise or lower the leg to adjust the least amount. Now there are some that will tell you this is a no no. It will twist the frame and could cause a problem. If this was true the frame will bend or twist when you go over some really unlevel ground. This is your call. Once you have the landing gear on the ground and the trailer off the TV you will need to raise or lower the front using a level on the on the inside floor, stove, basement floor, inside of the fridge or where ever you want to determine is the place you want level. Then if you have rear stabilizers you can drop them and maybe raise the nose of the trailer a little bit to place a small load on them to help steady the trailer.
Now, this is how I did it. I hope it helps, but it did work for me.
This is what I did.
BC