  We present a practical guide to Smoothed Particle Hydrodynamics (\SPH) and
its application to astrophysical problems. Although remarkably robust, \SPH\
must be used with care if the results are to be meaningful since the accuracy
of \SPH\ is sensitive to the arrangement of the particles and the form of the
smoothing kernel. In particular, the initial conditions for any \SPH\
simulation must consist of particles in dynamic equilibrium. We describe some
of the numerical difficulties that may be encountered when using \SPH, and how
these may be overcome. Through our experience in using \SPH\ code to model
convective stars, galaxy clusters and large scale structure problems we have
developed many diagnostic tests. We give these here as an aid to rapid
identification of errors, together with a list of basic prerequisites for the
most efficient implementation of \SPH.
