You know that list that comes out that has brief synopses of the series for next season? That's typically what I'll reference first to see if the show is going to have a plotline that I'm going to enjoy. Then I'll check out MAL or Anime News Network reviews for the first couple episodes. If a show passes those tests, then I'll try the first couple episodes. Usually (unless the show is really horrible) I'll then stick with it for the entire season.
Of course, anything with "Precure" in its title automatically becomes a "Watch" for me.