For those of you, like me, who were confused in the beginning (9/10 because the instructions pass by too quickly to be able to read) here is some clarification:
At the start, Mad Karate Man begins running toward a banker. Keep your eye at the top of the screen; a white arrow above the banker's head will appear on the right side and approach center. Click the mouse ANYwhere when the arrow hits center. This will determine how long your aerial assault will be (shown on the bottom left corner).
While in the air you must click on the banker high, med high, med low, and low. He will block with his briefcase. Early on there isn't much you can do about it since moving around it is difficult, but later in the game you will simply blow through it. While in the air attempt to hit the banker as many times as possible, accumulating combo points for successive strikes without blocking. This will determine how much power you have, measured in the bottom right corner of the screen.
When you land, click ANYwhere when the arrow is closest to the white portion of the arc, indicating the ideal 45 degree angle. This will launch the banker, and the game is afoot!
Use kicks to launch the banker higher, either by clicking the large button to his left or on himself directly. Clicking on ninjas does NOT use up power but in fact ADDS power, so do it often! It does cause the kick cooldown to restart, however.
Energy beam clears obstacles and accelerates the banker.
Early on you will depend entirely on luck to get combos, which is the only real method of gaining power. Power will allow you to use kicks and extend the launch, gaining you more points. Points will be used to upgrade.
Near the end of the game you will find that you can almost keep the banker up indefinitely if you are capable of consistantly clicking on the ninjas, gaining power.
My tip is not to kick the banker again until you've noticed that the +height numbers have stopped increasing. This indicates that you are at or past the peak of the arc and another kick will have the most effectiveness. It also allows you to kick ninjas in the meantime and refill your bar.
Another tip: Do NOT invest in the "Body Mass" upgrade (increases your max power) until you are consistently able to rack up combos. Similarly, until you have sufficient power and time in the air to destroy a briefcase there is no need to invest in lowering the briefcase's HP.
I suggest investing in time, air speed, and air power to start with to get the ball rolling. Whenever possible, upgrade final kick power, of course.
Hope this helps. Enjoy!