Chapters 1 and 2 of the SSET will help you to define your playing field. You can follow the summary in this page or visit the Creating a Sustainable Strategy and Management sessions of this Wiki.
Three steps to get started:
- Know the value of being sustainable.
- Make an organisational commitment.
- Define your playing field.
Know the value of being sustainable
You if don't know why you are doing it, you will not be able to get it done!
Before you get started, take some time to understand the value added by sustainability to your sport event.
You can build your own "business case" for sustainability by understanding the conections between your stakeholders interests/expectations, the major sustainability issues related to your sport and your event and the associated risks and opportunities.

Make an organisational commitment
Once you know why your event should be sustainable write a public commitment statement outlining your intention to organise a sustainable sport event and communicate this both internally and externally.
See a few examples by following this link.
Define your playing field
Assess your capabilities, identify the core competencies as an organisation and how they can best contribute to sustainability, look again at your risks and opportunities and define your playing field!
You may want to use the Sphere of Influence tool to help determine what you will or won't target.