The complex and far-from-intuitive issue of establishing how and when to act when manoeuvres are to be performed in space is discussed here in a simple graphical way. An analysis was made of the effects on the parameters of an orbit of low thrusts in three directions: tangential to the orbit; normal to it in the orbit plane; and normal to the orbit plane. An outcome is that, in order to obtain a desired effect, and at the same time minimize the undesired ones, it is better to use only a tangential thrust or only a normal one rather than a combination of simultaneous tangential and normal thrusts. Thus it is not necessary to investigate any alternative orientation of the thrusters. A manoeuvre can be accomplished by thrusts given either only once along the orbit path, or in more than one orbital point. Diagrams are produced which give a quick insight into the manoeuvre philosophy for both kinds of action.