I have received a lot of questions about what order you should do cardio or weights the gym. In fact, it really depends on the goals that you have. If you goal is weight lifting and bulking up or if it is running a PR half marathon, your answer will be different.
Generally, you want to start your workout with the exercises that will give you the specific results you are looking for. If you are hoping to run a 5 minute PR on your next race, you want to do your run training first in your workout so you are not too tired to work on sprints and form. If you had started with weights, your body would already be tired out before you could work on your cardio and speed.
If your goal is to bulk up, you will want to start your workout with a 5-10 minute dynamic warm-up such as jumping jacks, jump rope and mountain climbers or a slow jog. Then you will want to do your weight lifting during the first part of your workout. You can end with cardio work, it will just be at a lesser intensity than your weight lifting was.
Keep in mind that the order of your exercises really depends on how you feel when working out. If you prefer to do weights and then cardio, do that. If you prefer cardio and then weights, that is ok too. As long as you are getting to the gym or putting in your workout or run, you are doing what is right for your body. If your goal is simply to live a healthy lifestyle and get all around fitness for your body, then the order of your workout does not matter. What matters is your commitment to work hard everyday and do what is best for your body.