It all hinge on your goal. If your primary focus is strength/muscle gain, then follow a 5-10 minute warm-up with your strength training routine and execute your cardio work at the end of the exercise period. If you primary goal is fat loss, then it doesn't matter which you start with-many people like to start with cardio in order to get the body fully warmed up.
There are many arguments on the Internet about which one should be done first. Some believe that if you perform weight training initially, you will use up all of your carbohydrate stores in your body and therefore burn unconditional fat during your cardio session, however there is no truth in this type of workout routine. If your cardio sessions are rather intense, you may want to start with the strength training first for a couple of reasons. One, if you perform a long duration, intense cardio session; you may be too tired to focus on your strength training routine which would rise your risk of injury during weights and/or reduce your resistance training results. Lastly, carrying out the optimal strength training workout that addresses muscle imbalances, core and balance, etc... First will assist in ideal efficiency, and calorie burn during your cardio exercise.