No way. Don´t put your mind into a closed narrow box. There are main topics that will drive you through the whole thing, but don´t forget that creativity does not follow any rules. Yesterday I had one hour of spare time in the streets. So I walked around and played with the things that came in front of my eyes.
These are the resulting images:
As you can see, there are many different styles and topics. There are lines, boats, people, lights, holes and other things that attracted me to take a photo off. Even if you don´t use all this photos later on they are important as a visual diary (capturing the mood, the weather etc.) you can flip through to get some inspiration.