You're better be fast in the streets (or when you're with your impatient girl) - you'll never know what's coming your way. So be prepared. By this I mean to anticipate any upcoming photo well ahead and having the camera set up accordingly.
- Know you camera's dials inside out.
- Set ISO to auto or have it at a reasonable level according to the lighting conditions around you. Any EV compensation?
- Know your lens: Make mental pictures with the given field of view while approaching a promising scene and start arranging the foreground / background relationship. Busy backgrounds spoil a lot of pictures.
- Take the available scenic contrasts into consideration. Taking pictures without contrasts is in vein.
- How about depth of field? Enough or too much with the set aperture?
- Find your route. Where will you go or stand when taking the photo?
- How fast can you frame the shot? Try finding a video of Garry Winogrand. He frames (and handles his cam) in a split second! I'm far from being that fast.
- Forget about compositional rules but at least stop thinking too much about 'em.