Know the difference between a "Personal Shopper" and a "Stylist"
There's a big difference a personal shopper and a stylist. Contrary to popular belief, not everyone that claims to be a "stylist" on tumblr is the real deal. Personal shoppers get paid very well, but offer something completely different from a stylist's services. A personal shopper goes to a store on behalf of their clients, and edits a small selection of clothes that they are most likely to buy. That means you have to really know your client and his or her personal taste. Stylists, on the other hand, help create a client's image.
They come to you to put their best style forward. It's your job to make sure they look on top of their game. That means visiting showrooms to cultivate relationships with brands, designers, and publicists, attend fashion week, and have some tailors on hand who are able to custom fit gear for your client. If you're good, you'll be able to navigate the politics well enough to not have to pay for anything.