Here's my top ten for being healthy and fit:
1. Walk as much as possible - even short walks can be great
2. Take the stairs
3. Do some activity first thing in the morning - it gets the metabolism going
4. Get up from your desk each hour
5. Strength train - build those muscles
6. Minimize sugars and starches
7. Drink lots of water
8. Take up a new activity periodically
9. Exercise with friends/family - it's fun and you're more likely to stick with it
10. Join a gym
Keep in mind that activity is cumulative, everything you do adds up. The more you move, the better.