Never assume a driver sees you.

Learn to read the "body language" of cars to tell when they're about to turn. For instance, edging slightly to the side of the lane, irregular braking patterns...there are probably other things I cue off of that I'm not even aware of.

Related to the above, be aware that drivers almost never signal for a turn until they've actually started turning. Lack of a turn signal does NOT mean that a car isn't going to turn.

Watch for turn signals anyway.

If you are passing a line of stopped cars (especially if you are in a bike lane and in commercial areas), watch for breaks in the line. It often means that a "courteous" driver is letting someone from the other direction turn left in front of them. You may not be able to see that car and it will not see you. The break in traffic is often your only signal.