How do you beat Zero's missions on Grand Theft Auto San Andreas?

Zero's missions are some of the toughest, and, unless you are very lucky, you will try and do them several times before you achieve completion. It is just a matter of shooting skill in the first mission, and then skill with manoevuring the model planes and keeping an eye on the route and the time, etc.. I think the first two are hardest than the last. There is no easy way to achieve them.