Koder,
Find a large vacant parking lot, especially those with islands between the parking spaces. Practice making turns in both directions. Also, practice backing. If there are no islands in the parking lot, set out a few orange cones in a pattern(something like a traffic intersection). Take a family member, or friend with you to act as a spotter.
First, spent some time making left and right turns with the wheel cut as far as it will go to see if the trailer would jackknife going forward.
Next, try the same in reverse both to the left and right. Make sure your spotter is watching closely as to not run the trailer into the back window or cab of your truck.
Finally, after learning your limits of the combination, practice backing the trailer into a parking spot several times. This will help you while backing into a campsite.