Do anaerobic training!
There is abundant new scientific evidence, like this 2007 study, that clearly demonstrates there are enormous benefits to interval-type training. I now firmly believe that although endurance cardio training is important, it really needs to be part of a more comprehensive program that includes short bursts of activity at very high intensity, individualized for your specific fitness level.
The new evidence suggests that this may actually provide MORE protection against heart attacks than long durational aerobic type exercises.
Another major benefit of this approach is that it radically decreases the amount of time you spend exercising, while giving you even more benefits. For example, intermittent sprinting produces high levels of chemical compounds called catecholamines, which allow more fat to be burned from under your skin and within the exercising muscles. The resulting increase in fat oxidation increases weight loss. So, short bursts of activity done at a very high intensity can help you reach your optimal weight and level of fitness in a shorter amount of time.
It would be wise to have clearance by your physician if you are not in good shape before embarking on a program like this. However, you could start simply by walking and progress at your own pace.But this is a technique that should help nearly anyone who uses it.