You never need to move your mouse... first shot should be on the near edge of the second block.... (middle of screen) and let go when you are just coming up. If you get it right, for the most part your dude shouldn't ever go over the blocks... or shouldn't go that far. If you are going over the blocks, you are letting go too late.
If you are hitting the ground on the swing, you are firing too late.
P-