Little lifestyle changes can make a large overall impact on your health and fitness. Try walking the stairs or even walking up the escalator rather than standing. Don't fight for that close parking space, opt for one further away (which saves you stress and time, in addition to giving you a little extra walk). Little changes, such as these, add up...try it for two weeks, and I bet you'll notice a difference in your mood and energy!
I found that one of the most valuable things my dietician taught me was portion size. When she showed me the little plastic models of food, I was shocked at the size of them. They seemed so small! However, adding veggies, fruits, and all the other 5 food groups to the mix really makes a difference, especially since veggies and fruits serving sizes are quite large!
When reading serving sizes on labels, I like to cut the serving size listed in half and eat that much instead of the entire amount.