This paper introduces some improvements in 3D trajectory tracking and guidance design law of an unmanned aerial vehicle. The reference trajectory is generated on the basis of a prescribed sequence of waypoints defined in the flight plan. For this purpose, it is shown that using Frenet based frame and appropriate movements in turns arriving at the waypoints or maneuvers in transitions from one type of trajectory to another one lead to better global performance, in comparison with for instance the approach based on asymptotic output tracking technique previously studied and which involves the first or the second order differential dynamics of the tracking error. The global improvements are shown on the basis of the tests performed using a flight simulator, provided by the French Defense Agency, and which herein includes the implementation of the new guidance system. The flight simulator has been made running with the input parameters of the mini UAV called DRAC (Drone de Reconnaissance au Contact). The results are shown with no disturbances and in presence of wind as well.