Neglecting things is a big issue which needs to be addressed first.  
For your fitness regiment start simple
At home
When you get up (Look at youtube videos if you do not have a clue what these are)
- Stretch 
- calisthenics<p>In the office
Use a timer and every 90 minutes go for a 10 minutes walk.
You could also do chair exercises but that would depend on your sitting configuration.