There are leveling jacks
And there are stabilizers
Stabilizers do just that, stabilize. They do not lift, and are not designed to support much, if any, weight.
Leveling jacks, sometimes called "leveling stabilizer jacks", will (usually) be able lift and support some weight of the trailer. The BAL brand jacks that came on my trailer are rated to lift 5,000# each (there are 4 on my trailer). However, BAL also recommends that you not raise the trailer completely off the ground using the scissor jacks.
Regardless of which type you have, get the trailer level from side to side first. I would recommend to get some of the plastic leveling blocks. I like the Lynx blocks myself, especially now that they have a wheel chock add-on. They are real easy to clean off. If you need to raise it more than one block (1 ½”), put 2 flat on the ground and overlap another one on top of the bottom two. This will raise the tires 2 ½” off the ground and make it easy to drive on and off. I wouldn’t go any higher than 2 blocks because it may make it difficult or impossible for your stabilizers or leveling jacks to do any good without also adding some blocks under them as well.
It might be easier to move the trailer around to a spot that is a little more level.
You can also use wooden boards under the tires to level out the trailer. Make sure you use boards that are at least as wide as the tires are. A few half-inch and a few one inch thick boards should do the trick. You may be able to find some scraps at a local lumber yard for free. If not, and you end up buying an 8' long board, just cut it up into the desired lengths and you'll have some spares. You may want to consider painting or treating the wood somehow so it will last longer. For the length, consider if you will be using wheel chocks or not. If so, make the boards long enough to fit the tire and the wheel chock.
Once you have the trailer level side to side, unhitch and level it up from front to rear.
If you have “stabilizers”, put them down as firmly as you can to reduce trailer movement, but do not over-tighten as this may cause damage to the stabilizers.
If you have “leveling jacks”, you can use them to do some fine-tuning for getting your trailer level if the boards or blocks under the tires didn't get it close enough to level for your liking. Here is the process I have been using since 2001:
1. Lower the front of the trailer about one inch with the tongue jack.
2. Lower the rear leveling jacks until they are snug on the ground. If one side of the trailer is just a little higher than the other, crank the jack on the high side back up 1-2 turns.
3. Use the tongue jack to raise the front of the trailer to get the trailer level.
4. Lower the front leveling jacks until they are snug on the ground.
5. Raise the tongue jack slightly so that the trailer weight is on the leveling jacks and tires. Keep the tongue jack down in case one of the front leveling jacks fail.
You can also use this process to take some of the wiggle and bounce out of the trailer while you are inside. What this process does is take just a little weight off of the trailer suspension, which is where most of the wiggle and bounce comes from.
Some people will disagree with my method claiming it will torque or twist the frame and cause problems with doors or windows not opening/closing correctly. But I have confirmed this process with my dealer and the Fleetwood Service department, who all agrees that this process should not cause any of these problems if this process is done correctly. Check with your dealer or manufacturer to verify the correct leveling procedure for your trailer.
Make sure you have wheel chocks on both sides if you are on any kind of hill or slope. If you have tandem axles, use one of those wheel chocks designed to go between the tires, especially on the side that is raised up on leveling blocks. Camping World has a couple different varieties. Do a search for "wheel chock".