A practical guide to fitting correlation functions from lattice data

This guide contains a collection of the tips, tricks, and techniques that we have found to be useful when performing very large, correlated Bayesian fits of two, and three-point correlation functions for semileptonic decays, in this case $B\to K$ and $D\to K$. It is written explicitly with the use of gvar, lsqfit and corrfitter in mind, but many techniques are transferable to other fitting software, and other correlator fits. The guide is by no means comprehensive, and many problems can be approached from different angles and points of view. The intention here is simply to present ideas which may be useful to others.