Kor of Memory
Member
Winston's leap is basically just a big rocket boost in whatever direction you're facing, followed by losing all momentum when you contact the ground and splashing everybody around you.
So aiming his leap is mostly a matter of pointing your viewport along the parabola you want to travel on. If you point too low, you'll hit the ground too quickly. You want to point upwards. Kinematics, bro!
Also, you don't need to be on the ground to leap. You can jump first, then leap.
You can also save yourself from falling off the world by leaping upwards fast enough.