Often getting a pitch is quite straightforward: you just turn up, and if the space is free you can play there.
Buskers who play regularly in a particular place tend to make informal arrangements among themselves. If someone is busking where you want to play, just ask them what time they plan to finish, and if you can take over from them. The chances are they will be glad of the oportunity to take a break. Don't just set up right next to them and start playing in the hope that they will go away. You are more likely to really annoy them and everybody else who has to listen to the resulting chaos.
Regular buskers tend to get to know each other. In our experience what goes around comes around, and if you treat other buskers with respect and consideration, you'll generally get it returned. The opposite is also true.
