Which comes first: weights or cardio?

Cardio and weightlifting are two important components of effective gym time - the question is, which should you do first?

The answer:  weights come first.  If you want to walk on the treadmill or jog lightly for a couple minutes to help warm up before your warmup weight sets, that's fine - it's always good to get moving a bit, elevate your heart rate slightly, and signal your body that harder work is coming.  Running six miles before you start lifting isn't just a bad idea, it's dangerous.  Lifting when you're already tired not only encourages you to cheat and use bad form, it also increases the chance of injury or an accident.  Tripping and falling off the treadmill is bad; dropping an 80 pound dumbell on your chest is much, much worse.

Summary: weights first, then run yourself into the ground as long as you like.