The properties of transport of energetic particles in a strong magnetic turbulence have been investigated in the last few years mostly through numerical simulations, due to the technical difficulties of pursuing an analytical investigation. Moreover, previous approaches could only be applied to a limited number of turbulence power spectra. Analytical treatments have often the limitation of assuming a priori that the particle transport attains a diffusion regime, whereas it has been shown theoretically that different turbulence power spectra induce different particle behaviours in the diffusive regime. We will discuss the main assumptions made in the current theoretical treatments and how go beyond them, for instance, fluctuation computed along unperturbed particle orbit, validity to first order in magnetic turbulence, small ratio of particle gyroradius to turbulence correlation length, uncoupled wavenumbers of particle power spectrum, with the aim of extending the original theories and investigate the strong turbulence regime. We will also discuss those numerical simulations which can help to address these points. This work will be relevant for the propagation of energetic particles in interplanetary medium, at supernova remnant shocks, in the intergalactic medium.