Broken up by how you would like to approach it:
(remember, when we say "save", we're talking not only saving your environment but saving your money!!!)

Mild Sustainability - Basic absolute free things that can be done but save a lot!

Medium Sustainability - slightly more advanced as it requires some shopping, but saves even more!

Hot Sustainability! - This is it! The one which is not for the faint of heart. Once you step into this zone, you're in for a whole new life!