It is important to figure out where you are on the fitness ladder to ensure you are giving your body the appropriate amounts of activity.
If you do too little you will not see change.
If you do too much, too soon you risk injury or exhaustion.
You should always listen to your body and try to stay in a zone that is comfortable but still challenging. It will take time to build up the confidence to know what is right, but if you listen to your body you will rarely get it wrong.