Go to your favorite street. (If you can't go there physically, then you can visit in your mind).
Map it out on a piece of paper. Then describe (or otherwise document) everything in detail.
The shops, houses, street signs, trees, etc.
My favorite street is Regent Street in London. The best walk of Regent Street starts at Oxford Circus on the northern end and ends at Piccadilly Circus at the southern end. It is always packed with pedestrians...shopping, working, moving from one place to the other via cab, big red bus, bicycle, on foot. It's a haven for a street photographer. The people watching is second to none on Regent Street. My favorite place to sit and watch people hurry by is the Starbucks. I will sit on a stool facing the street, have a cafe latte and a chocolate muffin and snap away out the front window. The reflections can add some interesting effects to the images.
I love to hang out around Piccadilly Circus. It's really a hub of activity. From there you can walk to the West End and the theater district. It's packed with tourists taking pictures of the famous Eros Statue and the large neon sign (it's the equivalent of NYC's Times Square).
Regent Street is filled with upscale shopping. Including the world's largest Apple store and my personal favorite, Hamley's Toy Shop which is seven!! stories tall and has been around since 1760. Usually, they have something fun going on outside, like the bubble guy.
Regent street also intersects with Carnaby Street, another great place for people watching.
I love Regent Street at Christmastime. There are even more people than usual and the windows are decorated with such fun and festive displays. The lights and decorations above the street are pretty amazing too.
If you ever have a chance to visit London, spend a morning or afternoon along Regent Street and be sure to take your camera because you're sure to grab some amazing images. :)