Little Miss Curious (me!) decided to go find the answer, so I did two things:
1) When I was in New York, I went to the ModelFit studio which is one of the popular places where Victoria Secret Angels train. Unfortunately, I couldn't meet Justin Gelband (the head honcho) as he was out of town, but I did speak with his wife for answers and took her class.
2) I went to workout at a gym in Tokyo and spoke with the personal trainer Yokote Teiichiro of famous Peach John models. Peach John a lingerie company that is like the Japanese version of Victoria's Secret.
Both gave the same advice! Here's what I learned:
1) Models focus on doing exercises that involve twisting, and they make sure that their body weight is focused inwards.
Let me explain.
Imagine that you're holding a towel - when you wring out the towel, it gets smaller in size, right? That's what happens when you do twisting - you are training the muscle to become compact.
Instead of doing bicep curls which can build your muscle out, you can extend your arm and just twist it forward and backward to train it in and get the slim arm result you're looking for.
2) Focus on holding your body weight inwards to get long and lean.
As far as making sure that your body weight is focused inwards, one thing you can try doing is a lunge and ask yourself where you are placing your body weight.
If you're the type of person who is leaning your weight towards the outside of your foot to catch your balance, then you are building muscle on your outer hip. Instead, if you focus on putting your weight on the inner part of your foot, then you'll be toning your inner thigh (hellooooo thigh gap!).
3) Stretch yourself silly
It's also really important to note that they do a lot of stretching. Actually, I would say that almost half of the workout is about stretching because you want to make sure that you're prepared to train the muscle properly and that it will rebuild in a balanced way.
It's these little points that will make big differences overall to the results you get from exercising. Don't just go to a gym and start lifting random weights or running on the treadmill without an understanding of what kind of result those exercises will lead to. Doing less but strategically is a smart way to go about creating the body that you want.
If you want to do exercises that utilize these concepts, then try Pilates or even the Tracy Anderson Method.