I'm no expert but before babies I used to work out a lot and my hubby is a gym freak nice and fit at 42 yo do here is what I know:
- always do 30 min weights before any cardio. This will use up all the glucose / muscle glycogen you have and put you in fat burning mode for your cardio. Much more efficient to shed the fat
- always do weights!!! Light and more reps for lean look, heavy and short reps for bulk. Why weights? Because first you won't get saggy which even if you are skinny can look awful, but really because it will up ur metabolism a lot and you will keep burning calories at rest. More muscle = more fat burning. Simple.
- intervals are the best for losing weight. Never rest!!! Just work out another muscle group: you'll get a cardio out if it too I promise. That's kind of what P 90X is about and that's a great DVD. I know a ton of people including me who got really fit with this.

I'm just fed up with the CDs and I know by heart what tony will say so I need another P90X. Lol