Refer to the owner's manual of your truck to make an initial adjustment of the weight distribution bars.
The manual for my 2015 F150 states to measure the height to the top of the front wheel well with no trailer load. This is H1.
Attach the trailer with no weight distribution bar tension.
Measure the wheel well height again. This is H2.
Adjust the weight distribution bars so that the wheel well height is reduced by one quarter of the difference between H1 and H2.
Check that the trailer is level or slightly nose down. If not, adjust the ball height and repeat the previous steps.