The effect of the zitterbewegung consisting in trembling of trajectory of propagating particles may, in principle, be found in a variety of physical systems characterized by split kinetic energy dispersion branches. However, in a majority of material systems the effect is too weak to be observable. Specially designed semiconductor heterostructures representing optical microcavities with embedded quantum wells allow observing the zitterbewegung of exciton-polaritons that are optical cavity modes strongly hybridized with excitons in quantum wells. Here we show that external magnetic fields applied in the plane of the microcavity amplify this effect and allow for tuning the amplitude and the period of oscillations of polariton trajectories, thus being a convenient tool of control. These results pave the way towards realization of ballistic polariton transistors based on the spin-orbit effect, conceptually similar to Datta-and-Das transistors.