The website Television Tropes and Idioms (TvTropes) has seveal pages for fanfic tropes, some of which are staples of badfic. I've noticed that the pages "Draco In Leather Pants" and "Ron The Death Eater," which refer to when a villain is considered good, and also attractive, by the fandom, and when a hero is considered evil by the fandom, respectively, have ever expanding lists of fanfic where characters are ridiculously OOC.

I mostly look for more... racy fic than your average Sue, but I still look for other things on occasion.

What I usually do on fanfiction.net is exclude works under 1000 words, sometimes even works under 5000. Most of the things on the Pit are oneshots or just getting started, so it's hard to tell if they're going to be bad enough or long enough to be entertaining.

On AO3, I've found it useful to sort fics by how many hits they have. Oddly enough, the things with the most hits can sometimes be the worst fics around. AO3 makes it much easier to find badfic (or goodfic, for that matter) because of their tagging system; once you find a tag that has a lot of terrible things written for it, you can just search for that tag later.

Beyond that, there's a lot of reading summaries and hitting that "Next" button at the bottom of the page.

On the Pit, I set the ratings to 'all' and the language to English, which helps make things go a bit quicker. If I'm looking for an OC Sue, I add that filter on as well, but otherwise I just scroll and look for a summary that catches my eye.

If I'm in the mood for a particular type of badfic, I'll use the search bar and type in something like "lord potter' or 'veela malfoy' and go from there.

On Quotev, you can't swing a kneazle without hitting something hilariously bad, so for that site, I just bring popcorn and enjoy the ride.

Keep pressing "next". Make sure to go to different sites: for example, in the 40k fandom FF.net tends to have higher-quality content than AO3 in my experience, and other fandoms have it reversed. The larger your fandom, the more likely you are to find something, and the faster you can find it on average.