I get this question a lot: Should I do cardio first or weights?
There is a lot of information out there regarding how to achieve the best results from your workout.
The bottom line is to do what works best for you. If you find that you are too tired after lifting weights to do cardio or too tempted to skip cardio once you have done your weight lifting, then maybe it is best if you do your cardio first.
That being said, there is a bit of science behind the idea that you can reap more benefits by lifting weights before cardio. Basically, it is the idea that you may not have adequate stamina or strength to lift weights after doing cardio. Also, if your muscles are engaged, it is believed that you will burn more calories during and after your workout by performing your cardio after lifting.
But again, It is really more about preference. the most important thing is that you exercise. Do what works for you.