Top of the list: stay away from the investigators for at least the first couple of days of the case.
EVERY whodunnit I've seen on TV in the last few years has followed the same pattern. The killer turns out to be someone interviewed in the first 5-10 minutes of the show. So there
Seriously, though. Like most long-time marrieds, I've thought a lot about the perfect murder. I've come up with a half-dozen or so techniques that would probably work...