In this talk, I plan to present preliminary results of updated SM predictions for charm-meson lifetimes, their ratios and also the semileptonic decay widths, based on the Heavy Quark Expansion (HQE). In addition to the known contributions, for the first time we include the dimension-six Darwin term for non-leptonic charm decays and the first determinations of the dimension-six Bag parameters from HQET Sum Rules, including so-called eye-contractions and $m_s$-corrections for the case of the $D_s^+$ meson. The predicted observables are found in agreement with the experimental data though within very large theoretical uncertainties. Future prospects on the theory improvement are also planned to be briefly discussed