I've been Googling for a little while tonight, but I can't seem to find any rules on this.
Irregular ("strong") verbs seem to be pretty set in their endings: goest, dost. But when I get to something like "bring", it seems almost like "bringst" and "bringest" are equally valid, and I can't find any examples to lead me to one sort of rule or another. If anyone could shed some light on this, I'd appreciate it.