I review single dish "on-the-fly" mapping, both line and continuum, based on years of active research and support at JCMT. I discuss simple guidelines that ensure successful mapping and show why we may end up with systematics in our data due to the way we observe. Some of these "rules" and guidelines are documented in the JCMT observers guide and in short articles in the JCMT Newsletters. I will not cover bolometer arrays, like SCUBA, which are discussed elsewhere in this volume, but since arrays map faster, deeper and more reliably than single beam receivers, they provide a unique opportunity to investigate systematics in different mapping and reduction techniques.