Start running and strength training
Try to run in the morning. Begin with a slow pace at first so that you can maximise your mileage, and then increase your speed. Morning running will give you energy boost for the entire day and will also aid you burn more calories in the day; resulting in increasing your overall fitness level. In the case you cannot run, you can walk or jog as an alternative. On the other hand, do weight training to build strength if you have exercise equipment. This kind of training is ideal to perform in the morning when you get up. However, if you do not have access to weights, a substitute for that is to do sit-ups, pull-ups and push-ups.
To increase lung capacity and to strengthen leg muscles try to do more pace work on a walking track or run hills. These kinds of physical exercises are good for you because they help you enjoy a combination of both cardio workout and strength training. Moreover, jump rope as an activity to increase the amount of your air intake through the lungs. This is a very effective exercise for lowering your resting pulse, and it can improve your fitness level up to a decent extent.
Cycling and Yoga
Do some cycling on the roads or on hills to boost your fitness level. Biking increases stamina by helping you to work your heart and lungs for a longer, sustained amount of time period in comparison to running. It is also a good way to build lean and strong legs. You can also join a yoga class. Begin with a daily yoga schedule. It can be productive to improve your fitness level and is a great workout. It aids build, long, lean muscles, increases lung capacity and gives you a lot of extra energy.