Simple changes can make a difference, like walking where you would normally drive, taking the stairs over the elevator...but one thing you may not have thought about is your desk. Some people work jobs where they rarely leave their desk, even work through their lunch. This can lead to back strain, muscle weakness and of course excessive inactivity.
So maybe it's time to look at an alternative desk option.

The benefit: your core will be activated the entire time you are on the ball, helping to keep you in good posture. If you slouch, you'll probably fall off.
The potential problem: Sitting too long on a ball can still have it's consequences. If you have a weak core, it could put a lot of strain on your spine, leading to other back problems.

The benefit: A whole lot less sitting and you can move around a bit.
The potential problem: If you have joint pain in your knees, hips or ankles, this position could get uncomfortable after a while. Have a desk that adjusts back to normal so you can alternate between might fix this.

The benefit: More exercise!
The potential problem: Hope you don't space out because you might go for an unexpected ride if you didn't turn it off.