When starting a new workout out plan it is key to have an exercise strategy laid out before you begin. Your plan should be heavily influenced by your goal(s). Setting a proper strategy is important, it insures the direction you are heading in will lead to your desired target.
It is important that you set up realistic goals that correlate with the effort you are willing to give. You can't expect to lose 15lbs in a month if you are only willing to exercise three times a week for thirty minutes. Working out 5-6 times a week for sixty minutes would be a better way to reach that goal.
It is also key that the actually exercises you do match with the desired results you are expecting. Even if you do decide to workout six times a week for an hour, if you set up a poor routine it will greatly diminish your chance of reaching your goal. The timetable you set to accomplish your objective will be prolonged and this may lead to discouragement and/or quitting because the goal feels unattainable.