Have you researched into existing designs that consider environmental, economic and social issues to give you ideas for your own design?  
Have you considered which social, economic and environmental sustainability issues are important in your project?
Want to know what social responsibility means?
Want to know what environmental responsibility means?
Want to know what economic responsibility means?
Have you asked your different stakeholders  which sustainability issues are important to them?
social issues that effect them
economic issues that effect them  
environmental issues that effect them  
Have you drawn conclusions about which sustainability issues it will be appropriate to consider in your project?