  A general self-consistency approach allows a thorough treatment of the
corrections to the standard mean-field approximation (MFA). The natural
extension of standard MFA with the help of a cumulant expansion leads to a new
point of view on the effective field theories. The proposed approach can be
used for a systematic treatment of fluctuation effects of various length scales
and, perhaps, for the development of a new coarse graining procedure. We
outline and justify our method by some preliminary calculations. Concrete
results are given for the critical temperature and the Landau parameters of the
$\phi^4_d$-theory - the field counterpart of the Ising model. An important
unresolved problem of the modern theory of phase transitions - the problem for
the calculation of the true critical temperature, is considered within the
framework of the present approach. A comprehensive description of the ground
state properties of many-body systems is also demonstrated.
