  We generalize the two-particle self-consistent approach (TPSC) to study the
extended Hubbard model, where nearest-neighbor interaction is present in
addition to the usual local screened interaction. Similarities and differences
between the TPSC approach and the Singwi Tosi Land Sj\"{o}lander (STLS)
approximation for the electron gas are discussed. The accuracy of our extension
of TPSC is assessed by comparisons with Quantum Monte Carlo calculations of Y.
Zhang and J. Callaway, Phys. Rev. B \textbf{39}, 9397 (1989). We observe that a
positive off-site interaction enhances staggered charge fluctuations and
reduces staggered magnetic order.
