The most important thing to look for is the safeties. If there are two safeties deep, you know it's a cover 2, one safety deep, it's cover 1, and so on - you can send a man in motion to find out if it's man or zone, and hard count to pick up the blitz.
Personally, if I see the defense in cover 1 or cover 0, I spread the field to put as much pressure on the defense as possible; give myself a quick passing option (because you can pretty much expect the blitz), and send at least one receive deep (all he has to do is beat his man off the line).