Most will level side to side first using planks of 2X8 or the Lego's for leveling. This is done first as you use your Truck to push the RV onto the boards/blocks.
Once level side to side you will want to drop the landing gear to the ground or onto shallow blocks if you use them. We used square pieces of 2X8 and it worked just fine.
The electrical adjustment on the landing gear will lift the RV off your truck and hitch. Be sure you block your wheels to avoid rolling and dropping the RV on the truck bed-walls. Then pull your truck out slowly.
Be careful and take your time. Don't let anyone/anything distract you from your process. :)