I decided on my first subject: feet.
Mainly people's feet. I've taken a dozen photos of my own feet, at various times of the day. I even have some close-ups of my toes. Then over the weekend, I started sneaking in shots of other people's feet.
I didn't want to be obvious, so I turned off the flash on my cute white Canon Ixus i and held it like a wallet or cigarette pack. Then I put my jacket on my arm, partially covering the camera.
After an hour at Glorietta, I concluded that it was easier to just sit down and let people pass and stop by, then click. Usual problems include: wrong focusing and moving subjects.