Weight training

If increased strength and/or muscle size is the focus then resistance/weight training is the path to follow. This encourages the body to adapt by imposing an increased demand on your muscles. This can be achieved by simply contracting a targeted muscle for five seconds or by using weights or everyday items such as paint or soup cans to contract the muscle fully.

In order to achieve continued gains you will need to increase the resistance or weight you use over time, since your body will become accustomed to the initial starting weight and will need to be constantly challenged.
An important thing to remember with resistance training is that unlike cardiovascular exercise, you shouldn't work the same muscles every day. Always take a day rest between resistance training sessions so that the body has time to rest and recover.
However, if you are determined to see big improvements in your body shape, you can work different muscles on different days so that daily training is possible.

In order to improve overall fitness levels it's best to do a mixture of both cardiovascular and resistance training. However, please remember that if you are unwell, you should not do any strenuous exercise.