There's lots of ways to improve your fitness level and your general well-being.
The first thing to do is to figure out if you have a good balance:
One day is 24 hours; 8 hours for sleeping; 8 hours for working and; 8 hours for playing and relaxing. Is that how you spend every day?
The second thing to do is to get that balance. This is where you work out your priorities, do some goal setting and find some time management skills.
Another thing to do is to write down, or at least think about, everything you eat for one week. At the end of the week review your food choices. Did you drink lots of water, eat plenty of cereals like brown rice, eat lots of vegetables, some fruit, a little bit of dairy or nuts, fish and a little bit of meat, a little vegetable oil and no soft drinks, cakes, biscuits, lollies (or maybe just one in the week)?