So here is my advice to our heroes, addressing the Top 3 Mistakes that should probably be avoided whenever possible:
1. Do Your Research.
If our heroine is hob-knobbing with vamps, weres, fay, and all manner of supernatural folk, she should learn all there is to know about them. Instead, I see too many protags hanging out with very dangerous creatures, only to discover that they have unwittingly made a crucial faux pas and must now pay the price.
Yes, we want to cause trouble for our heroes, but that doesn't mean they have to stumble around blindly before accidentally falling into a big stinking mess. It would be far more interesting to present a situation where the heroine must make the choice to break a rule which she knows will have consequences, but she does it anyway for a good reason.
*Characters who have just been introduced to a new 'world' in an original novel get a pass on this one, but they should have things figured out by book two.
2. Don't give out key information.
Our hero is in contact with someone whose suspicious activities have put them in the middle of the mystery. A bad move is to have them tell said party what's being done to solve the case and where they can find the hero in order to get together and answer some questions, regardless of whether they've known each other for a while.
If we need the bad guys to find out certain information about the hero's activities or whereabouts, there has to be a better way. Set up a spy in the hero's camp, or have them be a tech-savvy kind of villain who has pre-set surveillance and taps into street cameras. Anything but a blabber-mouthed protag please.
3. Hold your lovin' until the appropriate time.
All hell is breaking loose, people are dying and danger lurks around every corner. If the heroine can't figure out what's going on soon and stop it, the whole world as we know it could end. So how about a night of nooky with the guy she just met instead of searching for clues? Bad idea.
I'm not saying romance is never appropriate, even in bad situations, but I can't stand to have a lead who is more interested in her budding relationship than the crisis at hand. Worse if it turns out that the supporting cast is doing all the legwork in the meantime, or the villain has gotten away with something terrible while the heroes were, um, distracted. All I'm saying is think hard about the fallout before taking time out to do the nasty.
None of these flubs necessarily put our heroes in the category of TSTL, but why not avoid that slippery slope altogether. What are your pet peeves when it comes to characters making the wrong choices in any genre?