Before you start exercising you should think about what you are trying to accomplish. Setting realistic and measurable goals is a useful tool in starting and maintaining an exercise programme.
It's a good idea to set clear plans like "I'll do 20 minutes of moderate cardiovascular exercise such as biking or walking, 3 times a week for the next 3 months, in order to lose 10 kilos". You can then adjust the goal if it seems you might not manage it exactly as hoped. Better to adjust a goal and keep on going than just feel defeated and pack it in!
There are three important components for any exercise routine.