Accretion onto neutron stars powers the brightest X-ray sources in the sky, offering a unique opportunity to test strong gravity and ultra dense matter. The luminosity and energy spectrum of neutron star low-mass X-ray binaries vary in a wide range of timescales. On the short timescale side (seconds to milliseconds), I will show and discuss results on the rapid X-ray variability of two accreting millisecond pulsars: kilohertz quasi-periodic oscillations in XTE J1807-294 and extremely strong broadband noise in IGR J00291+5934. On much longer timescales (hours to weeks) these systems switch between different accretion states, which reflect different configurations of the accretion flow. I will present a systematic study of the luminosity, spectral and variability properties of such accretion states and discuss the main results of this work: i) the luminosity of state transitions varies by more than one order of magnitude among different systems and ii) some of the variability frequencies show a universal anti correlation with the hardness of the energy spectrum.