One of the most important ways to learn how to do things, is by becoming familiar with how not to do things. This has been my (sometimes unfortunate) mantra in life. Perhaps it's because I'm hard-headed, perhaps it's because I've never been good with the phrases "you must/don't ever." Either way, the advice is sage. Consider: I learned how not to get Danny Wood (member of the 1994-big-haired-Hannah's fantasy life/New Kids on the Block) to fall madly in love with me by stealing his mail then showing up on his doorstep all knight-ess in shining armour to return it. Because that, my friends, is a felony. One thing not to do gets me closer to the one thing to do, yes? Perhaps, but first I have to make bail.
And back to writing. When it comes to writing mysteries, in particular, throwing out the occasional red herring is a good thing. Creating the literary equivalent to a flashing red arrow to your killer on page two goes into the not file. Ditto with tossing in a last-page twist killer who we've never met up until that moment: "ah ha! The killer is Sally's Uncle Hal who was thought to be sheep herding in Alaska all this time but had some sheep herding grudge from way back, inspiring his murderous rampage!" (Perhaps his issue was that sheep don't thrive in Alaska and even if they did, they'd be really hard to find in the snow).
I'm currently writing my 8th mystery, but I'm still learning. Like yesterday, I learned NOT to splash coffee on my laptop, lest the keys stick in the cinnamon-brown sugar laced mess and, perhaps a bigger lesson, it fries the crap out of said computer's innards and you will cry. A lot.
Obviously, I shouldn't have been saving money for bail (I'm smart enough to never repeat a lesson and I'm mostly over Danny Wood). I should have been saving for a beverage-free laptop.
Or a sippy cup.