Towing with F250

I have a '95 F250 that I am using to tow a 16 ft. trailer. When the trailer is hooked up the truck "squats" slightly. It's not that bad, but it's enough that when traveling at night the low beam lights are pointing where the high beams should be and I've been making lots of friends with the cars that I follow. What is the best, easiest way to level the truck? Thanks, John