The kinds of activities that you do in order to maintain your physical fitness will depend on the particular fitness level that you are comfortable with. If you have not exercised very much in recent months, then you will not want to start your exercising by running three miles every morning. Setting your goals well beyond the level at which you can actually perform is a good way to get discouraged early on and give up trying to achieve physical fitness altogether. It is best to be realistic when you begin exercising, so try not to overestimate your fitness level.
For those just starting a plan to increase their physical fitness, it is recommended that you begin with just a moderate level of exercise. Try walking around the block each evening, for example. Only swim one or two laps in the pool. As you do these things, try and increase your speed each time you perform the activity. Over time you will find yourself being able to accomplish your exercise plans more quickly, and you can even begin adding extra laps to the pool or extra laps around the block.
When you feel as if such activities at the beginning exercise level are too easy, it is time to move on to some more intermediate exercises. It is at this point that you can consider adding some weightlifting to your routine. You do not have to lift hundreds of pounds, just enough to begin building muscle, which will help you burn fat and maintain your weight even when you are not exercising. Consider joining a gym or other fitness studio if one is accessible to you.
At a more advanced fitness level you will want to move on and increase the variety of exercises you are performing. It is also wise to seek the help of a personal trainer or just a friend who is more knowledgeable about physical fitness than you are. Either person will be able to give you the tips and tricks you need to advance to the next level.