Gradually increase, and I mean gradually. There is nothing worse than starting a brand new fitness regime and you injure your knee or foot or shoulder. Take it easy and be sensible. If, however, you have been training fairly hard and want to start something new, start slowly also. Just because you could run 25km in 1 hour 40 minutes does not mean you can shuttle up and down a basketball court without the possibility of an injury.
Food is extremely important when wanting to look good.
Pack your own food if possible. The more you eat out the less in control you are. Try and stay away from sugary fruit juices and soft drinks, protein drinks that carry high kilojoules and try to eat some more fruit between meals to keep that fire that is your metabolism burning. Finally, if after all this you lack motivation and a desire to look good and feel great get back in the bedroom.