I can tell you how often I do it, & you take it from there.
Measurements I used to do weekly, but I now do monthly. Just because I now also weigh monthly instead of weekly. I really recommend you measure when you weigh, right afterwards so you don't forget. (By saying this, I'm assuming you don't weigh in daily; I don't think it'll be of much use to measure everyday.) Pick a set of measurements to take and keep a log, just like you do with weight. Make sure you've got a good tape measure, and get down to at least the quarter-inch in your measurements, because sometimes changes are that small. (I use all the little slashes on the tape measure.
I have one photo from a couple of years ago that I keep as my baseline picture. I'll be honest, I don't take pictures with any great regularity. I do
always take one before starting a new exercise program, and try to take them at least monthly after that. I have a digital camera with a self-timer, though, so I'm free to take pictures of myself at whim.
I make sure to strip down to a bra & panties to take the photos, or at least a bra & shorts. I take headshots too, since I'm seeing the most change there. Those I do when I do my other photos.
You'll find something that works for you. I also, as I said in another thread, go by clothing fit. I don't have many bottoms, so I wear a few pieces constantly (I'm really
picky with my clothes), and I notice when the fit changes. In the waistband at least. It takes me a lot longer to notice pants/shorts getting baggy in the legs.
And now that I think of it, you're right with baggy not being so much of a style with girls. It's just that I've always had more guy friends.