To be honest if you are looking to lose weight I would suggest that you try doing it this way:
5 minute warmup on rower or treadmill
large muscle groups ex. squats, lunges, pushups
finish off with 15-20 mins of cardio.

I have been doing it this way for a year now and lost a lot of inches off my body by doing cardio second. I also used to focus on tiny muscle groups but it didn't do much justice for me. I found that when I stuck to heavier weights and larger muscles groups (legs, back) I burned a lot more cardio. If you want more details about my workout this is the one I have been following: http://www.trainerpack.com/busy-girl-workout-p-43.html

I find that if I don't work up a sweat then I don't really get much results. By doing a longer warmup you will rev up your body more and end up burning more calories.