4) Do try to confuse liturgy and cult practice with history. For instance, the mystery religions and Christianity were both underground movements, so they had to operate in similar sorts of ways. This doesn't make them similar in other ways, but pretend that it does. Sacred meals and ritual washing are as old as religion itself so the fact that Christianity employed them as well as pagans (not to mention Jews) is not surprising at all. Make it sound like a complete revelation. For instance, if Mithraists shared a ritual meal with bread and wine (and meat too, but never mind that), make it sound astronomically unlikely that Christians should have done the same unless they were borrowing from Mithraism.
5) Assert that totally different things are in fact closely related. For instance, Mithras was sometimes represented by a bull. Say this is the same as Jesus being called the Lamb of God (one is a symbol of sexuality and strength, the other of innocence and humility, but never let facts get in the way of a good theory). Compare the Mithraic ritual of taking a shower in the warm blood of the aforementioned bull with Christian baptism with water. Mithras was born as a fully-grown man from solid rock; call this a "virgin birth." Claim that the thieves crucified with Jesus are the same as a pair of torchbearers that appear on some illustrations of Bacchus.
6) For goodness sake, do not mention the things that really made the pagan mysteries interesting. After all, in your work of showing that Jesus and Bacchus are one and the same, you will lose everything if you let on that Bacchus was the god of drunkenness and his worship involved getting plastered and having sex with anything in sight (goats being a particular favourite). In fact, keep sex out of it altogether. Yes, sex was the central feature of an awful lot of these pagan rituals but that is not the point you are trying to make.
7) Avoid up-to-date scholarship that will probably pour cold water over your vaunted theories. One particular problem to ignore is that the Persian Mithras was much earlier and had almost nothing to do with the Roman god of the same name. Worse still, the Roman god only became widely worshiped after the birth of Christ, so cannot have been a model for Jesus at all. Also, take Sir James Frazer and Francis Cumont seriously, even if today's scholars do not. You will find plenty of other 19th-century and early-20th-century writers with a bone to pick who can support your wildest speculations. Finally, don't worry if some of the evidence, like the picture of a crucified Bacchus on the cover of your book The Jesus Mysteries, turns out to be fake. It is not your problem, even if you knew about it in advance.
8) Do not worry if not everyone agrees with you; you can always dismiss the dissenters as Christian apologists or as those unable to cope with your earth-shattering ideas. And don't panic if someone turns up arguing about primary sources, dating evidence, footnotes, and boring stuff like that. They are probably in the pay of the pope. Using this guide, you should be able to produce as many parallels as you require in order to convince even the most blinkered of readers that Jesus was actually a pagan god-man.
As you can tell, I am not impressed by the pagan myth hypothesis. It is telling that in spite of their vast amount of learning, their hostility to orthodox Christianity, and their willingness to allege that much of the New Testament is fictional, not even John Dominic Crossan or Bart Ehrman have any time for the idea that Jesus was made up of pagan motifs. Nor indeed do the vast majority of liberal scholars. The pagan myth hypothesis is firmly outside the pale of modern scholarship. That's also the reason why refuting authors like Tom Harpur tends to be left to Christian writers. Academic historians just don't think it is worth wasting time on anything so obviously wrong.
Editor's Note: For other online sources of information on the pagan parallels theories, see this detailed examination of various pagan deities and whether their stories coincide with that of Jesus, this note from William Lane Craig, or (as a more specific example) this response to the Jesus-as-Mithras claim, or this article from Ronald Nash. For book-length responses, consult R. T. France's The Evidence for Jesus or Nash's The Gospel and the Greeks.
The third part of this series will turn to the claim that Jesus is probably mythological because there is very little about him in the writings of Paul.