traveller has yet another how to write fanfic
post, which has some good points (and some bad ones) but IMO is mostly notable for the link, deep in the comments, to David Foster Wallace's article
Tense Present. Nominally a review of a usage guide, it really uses that as a jumping-off point for an entertaining discussion of usage rules, who gets to make them, and why they matter. The article's a few years old now, but no less worthwhile for it.
Go read it for the phrase "barrel of drugged trout," if nothing else.