Starting with cardio or resistance training (weights) can vary depending on your current fitness goals. A general rule of thumb is that after your warmup, you always start your workout with the area you are trying to improve the most.
Resistance training is beneficial to increase your lean muscle mass because, unlike cardio, it assists your body in fat burning even when you are at rest. I firmly believe that there is more than one path or way to lose weight and “what works best” can vary from person to person depending on where the person is and what they are capable of doing.
If your goal is to increase muscle size or increase lean muscle, then you should start with weights. If your goal is to lose weight or increase the duration of your cardiovascular workouts, then you should start with cardio.
When I first started losing weight, I was losing weight solely off of modifications to my diet. Losing weight boils down to burning more calories than you consume – you can do that with diet, exercise, or a combination of both. However, it is tough to out train a bad diet, so it’s important to be mindful of your diet and food consumption as well!