Modeling agents can be hard to impress in the start. So...The best idea is to start by being your own! I think of my own modeling pursuits as a marketing pursuit, with daily and weekly and monthly goals.
I didn't get started working with agents until a year of modeling on my own and trying to figure out " What is modeling and how do I fit in?"
Since then the modeling world has changed and digitally, and through the web a girl can be entrapped and enticed with being a model, but getting the modeling work, working with brands and magazines is a whole other world and it involves marketing yourself the right way to agents, to magazines, and being smart about how you sell yourself.
Before you start considering modeling agencies I would look at yourself and understand if you also know how to market yourself. Are you driven? Are you willing to seek out your own modeling work? Can you manage mailing your photos to magazines? Are you just modeling for the ego and fun and money, or are you modeling because you like it and know your can too!?
I enjoy seeking out my own modeling work and seeing results. I enjoy knowing that the agent is important, nice to have, a bonus...but I can also seek out my own work and I have no problem seeking out magazine editors, and brands I want to work with and trying to get intouch with them and see meetings and photoshoots and exposure an modeling jobs result from my own persistance!
Then you can take this effort you put into yourself and bring it to a modeling agency, a talent agency, a casting director, and have a better chance to be booked because you weren't bossed around, told what to do, but you learned it for yourself!