Write the worst plot you can possibly think of. Toss every trite turn into it. Use every cliche. Bald plot devices should be de rigeur. Pack it as full of dreck as you possibly can; brainstorm the most abundantly-used or annoying plot and dialogue tricks you can remember from every source. Joyously abuse language, metaphor and imagery.
Is there any point to this other than having a ton of fun? Well, sure, although I think the fun is reason enough to do it!
First, this can help to remind you that it’s a lot easier to find bad writing when you’re deliberately looking for examples of it. When you’re looking at your own writing and hoping to find it good, you’re less likely to ferret out these things. Instead, you could try turning it into an entertaining exercise in pointing out the flaws, as though you were snarkily pointing out the flaws in a late-night movie you stumbled across on TV.
Second, this can also remind you that many overused plots and plot devices became thus because they worked. We overuse the things that work. We take advantage of plot devices and shortcuts because they make things easier on us. Knowing this helps us to find alternatives that serve the same purpose yet seem more elegant, fresh and original.
Third, it can be frustrating at times to not be able to use some of these cultural shorthands. Sometimes it helps to get them out of your system all at once.
And finally, if you write all this stuff down in a hurry, free-writing it, you’ll find out which pieces of trite material are lurking most readily in your brain. This is probably a good indication of what you’ll need to watch for in your own writing. Make note of those types of mistake that show up most often, and turn them into a checklist for your own proofreading purposes.