I start with tithing. Taught the kids that even if they only get a dollar – 10 cents goes back to God (or charity or whatever your Higher Power is). I know that sounds like it costs money – but I treat it like a tax – it was never my money in the first place.
God can do so much more helping you with your 90% than you can ever do alone with 100%.
After that, freecycle your unloved stuff. Pay compliments, verbalize appreciation (I don't do this enough). Take the shopping cart back to the store instead of leaving it for the baggers.
Take a few seconds to pick up the trash left behind by others when you visit a park.