Bring your own mug to the cafe and carry your own water container (read about the ultra-cool reusable water bottle and coffee cup here and here).
Collect all of your trash each day and so you can see how much you produce.
Try to go a month without making any purchases other than food and energy.
Join Freecycle, where you can give away what you don't need and get second-hand stuff for free.
When the activity is fun, good for
Never use your car for a trip of less than two miles. Walk or bike. Notice the benefits to your physical fitness.
Swear off plastic bags.