as a girl, it's important to know your limits on what you're lifting. Because although muscle burns fat, if you don't keep up on building your muscle (or rather, tightening what you've already got) your going to watch that that was muscle turn into fat! What's a girl to do?
Start small and keep it that way. Do short reps with light weights - I'm talking about arms here, ladies - and avoid anything that's too strenuous. Typically, that should be anything that's over ten pounds. If you are trying to build muscle as opposed to tighten, this is obviously a mute point. But for those who are trying out the lifting thing for the first time do not think that more is merrier. Quick, light and repitive. That's what you're looking for.