Shop windows, bus windows, café windows, phone box glass. Shoot through them. You get reflections, distortion, colour casts, layers. The subject is simultaneously inside and outside the frame.

Raindrops on glass add texture. Dirty glass adds grain and mood. Clean glass nearly disappears - use it to shoot into spaces you can't physically enter.

Watch for: your own reflection. Position yourself at a slight angle to eliminate it, or lean into it and make it part of the picture.

The point: glass separates you from the subject. That separation is sometimes exactly what the picture needs.