To accurately predict how a sci-fi show will do, you'd need either a time machine or a bathtub full of precogs. Sometimes you get Star Trek: The Next Generation; sometimes you get Star Trek: Enterprise. It's confusing.
This season, seven sci-fi series are being canceled or have already received a pink slip. Fox's underrated Fringe will finish its run with a half-season slated for the fall while that same broadcaster's Terra Nova has gotten the shove and will be shopped around to other networks. Eureka is finishing up its run over the next few weeks on Syfy, and Syfy has also announced that Sanctuary is not coming back. Then there are the series that didn't show up on the schedule for this coming season: ABC's misbegotten The River, NBC's meandering Awake* and Fox's midseason replacement Alcatraz.
Some of these shows were good tries that fell flat; some of them were interesting enough to skate the edge of cancelation until their luck ran out; and some of them are respected success stories whose time has come for one reason or another. Looking back (and forward), here are a few things we've learned about how to send your speculative fiction show into its final orbit.
*I understand that Awake is perhaps more a psychological drama, but I'm still going to call it sci-fi because it relies on the conventional science fiction understanding of parallel universes—and nobody knows what goes on in someone's head during a psychotic break, so it's speculative fiction about biology, which is science.