Training for fitness can vary tremendously depending on whether you just want some measure of aerobic fitness so that your every day chores are easier to do and you feel more energetic and trimmer, or at the other end if you want to compete in fitness competitions.
In the first scenario, a combination of aerobic and resistance training exercise routines done for an hour or so three to four times a week will do the trick. Along with fine tuning your nutrition and lifestyle, you’ll look fitter and more buff. Other training methods including shorter training sessions using high intensity training and high intensity interval training using cardio and resistant training regimens. These methods can be useful for those with limited time to train but I don’t believe that they’re as useful in the long run as more traditional training regimens.
If you’re more serious, up to the point of competing, then you still need to do both resistance and aerobic training, but you’ll be working out harder and longer. In both cases you can use the Metabolic Index to follow your body composition progress, and various methods to find out if you’re fitness level is improving.