The American College of Sports Medicine has recently released recommendations about the quality and quantity of exercise.
Use them to assess your current fitness program and make changes if necessary.
Aerobic training
5 days a week of moderate-intensity exercise, 30-60 minutes a day, at least 150 minutes a week, or 3 days a week of vigorous-intensity exercise, 20-60 minutes a day, at least 75 minutes a week.
Resistance training
2-3 days a week, 48 hours between sessions, 2-4 sets per exercise, 8-12 reps per set (10-15 for older adults just starting exercise), 2-3 minutes of rest between sets.
Flexibility training (stretching)
2-3 days a week, hold each stretch for 10-30 seconds, repeat each stretch 2-4 times.
Functional fitness (Pilates, 
tai chi, yoga) 2-3 days a week, 20-30 minutes a day.
If you can maintain an acitvity schedule that achieves these recomendations you will be well on your way to a fitter and healthier year in 2012.
Good luck.
