How to design the structure of a program in Object Oriented Programming(OOP)?

I'm fairly new to object oriented programming and am working on a project currently in Java (although this question applies to any OOP language really) - I'm having problems planning out the structure of the program and was wondering if someone could give me some advice.

The scenario is a bike race and the program is based around the people involved in it (so I was thinking cyclists, spectators and organisers would be some of the classes?) I'm struggling to determine the objects and in particular what the relationships would be between them in this program? I'm making out a diagram so a clear understanding of these things would help a lot.