A great place to find open minded ppl that you could practice your readings on is the public library. You'd really be surprised how many you can do in a day if you're personable enough.
Also, a book store. When I was first beginning to read the cards, I hung out a lot at our Barnes and Noble, which was a MASSIVE store. I picked a table in the corner and had my cup of tea from their cafe and would throw the cards, reading for myself and many people would come and ask me to read for them. It was also then that I decided to make up some business cards and I'd hand out two of them--one to keep and one to pass along to a friend, to each person who asked me about a reading.
Another great place to 'advertise' is at colleges. If you have some business cards, post them on a bulletin boards wherever they have them (generally in the main school building or each of the dorms). I would only post a few cards, 3-5 of them. College kids are quick to pick up on having a reading--and I would offer them a discount reading for only a few dollars. (since college kids are also generally poor).
Then, of course, stores, cafes--especially coffee and tea shops--you would need to speak to the manager there. And, then there are bars and some restaurants where you can offer readings at, after speaking again to the managers. They generally would ask for a portion of your money received. Mom and pop type restaurants are generally your best bet.
Another fun one is chat roulette. However you will probably have to do several readings for an onslaught of flaccid penises. But it is the risk you take on the roulette.