Remember these key principles for success in your exercise:

• There are no good or bad exercise. Rather it is the right exercise for the right person, at the right time and performed the right way.
• Exercise is a stress and every session has a cost. Balance your training with the right amount and quality of recovery to ensure the effects are positive.
• Fitness is made up of many factors. The fitness to run a marathon is very different from that required to sprint 100m, throw a discus or compete as a bodybuilder. The type of training that you should do depends on your particular goals. 
•  Become clear about your goals and set objectives for your training, to achieve your best results. 
• Don't forget that Working In is just as important as Working Out