This is great! This usually means you’ve achieved success by regularly committing to aerobic exercises and you’re now ready to take your fitness activities to a new level.
If you’re truly looking to “tone up” your body, ultimately you will need to commit to two to four strength training workouts per week to achieve desired results.
Generally, there are three levels of strength and resistance training – strength (lower reps/higher weight or resistance), toning up (mid reps/mid weight or resistance) and maintenance (higher reps/lower weight or resistance). Before you start, spend some time in the weight room gauging the “rep” and weight levels that “exhaust” you to the point of fatigue for the desired goal.
Take a look at this post from Sparkpeople.com -- http://www.sparkpeople.com/resource/fitness_articles.asp?id=1033. I thought it offered solid direction toward getting started with a strength/resistance training program.