I watch--or if it's really bad, skip through--the first episode of just about everything. Some anime I feel confident I won't enjoy so I drop them immediately. Others get a "maybe" rating and I keep watching until I've seen enough to reach a conclusion.
More often than not, "maybe" anime never ends up clicking with me and I simply stop watching, sometimes without ever thinking about it. I'll put off the latest episode and just never get around to watching. I've seen enough anime to know that the first few episodes can sometimes be misleading, however. Punchline earlier this year, for example, which I thought was going to be vapid but instead turned out complex and interesting.
To each their own, though.
Personally, I generally dislike generic anime and anime with poor writing or a dependence on tropes and cliches. An abundance of those can lead to me dropping something unless it makes up for it in other areas. I'll admit that a really good character can sometimes keep me hanging on.
