I've been known to pick up anime on the basis of art. I also watch anime that have controversy around them (Like Gantz and Kodomo no Jikan), because I like to see if it's worth those twisted panties. And, of course, I've picked up several anime on the basis of adorable shota being present. And some anime I watch for a favorite director, animator or seiyuu.
Actually, plot is usually the last thing I look into. After all, it's hard to tell from a short blurb if a plot is decent. Kuragehime looks boring on paper, but was very well done. I'll watch an episode of anything if it comes highly recommended or fits one of my aforementioned descriptors. I'll stick to something for the plot, but it's definitely not where my initial interest stems from.