Signal your turns. It's one of those minimal courtesies that we expect from motorists (and on which our safety often depends). Some will argue that you should do all your signaling with your left arm, in accordance with longstanding conventions (e.g. forearm extended upward to signal a right turn). My wife thinks that too many motorists don't understand these conventions; so I point my turn with my leading arm, whichever that might be. Do whatever you prefer, but do signal.

Clearly, it's good advice to ride defensively ...
... since we here have evidence that at least some people you'll encounter on the street are willing to crash into you for strategic reasons.