The point of authenticity is that you just can't fake it. It is a state of being, and ultimately others will decide if you are authentic or not. Here are a few things to keep in mind:
1) Live Your Values
If one of your organization's stated values is honesty, then don't lie. Even a little white lie. It is better to say "hey, we've never done a project like that, but we'd love to have a chance to work hard for you" versus, "sure, we've done 30 projects like that" when you haven't.
2) Be Committed
If you are talking about being sustainable, then "walk the walk."
- Encourage carpooling, taking mass transit, or biking to work
- Provide reusable mugs or cups v. providing paper cups
- Grow a garden on-site, encourage employees to tend it, and then make the harvest available to all.
Look at internal and external processes -- where is there excessive use of resources, such as fuel, energy, or paper? Where is waste created? Overhauling inefficient processes will help you to build your sustainable rep and save you money.
4) Consider Affiliations
Look at the organizations with whom you do business:
- Do they treat their employees well?
- Are they a heavy polluter?
- Do they employ sustainable or socially responsible practices?
- Are they energy efficient?
- Do they have a good record on human rights?