You don’t need a fancy portfolio. If an agency takes you on, it will create one for you.
To get a good agent, email three snapshots of yourself (one smiling head shot, one non-smiling head shot, and a full-length bathing-suit shot), plus your measurements, to well-known agencies.
The top firms are in New York City: Ford, IMG, DNA, One Management, Women Management, Click, and Elite. There are dozens of legit smaller agencies that book big jobs, but just do your research to make sure they’re reputable.
Modeling schools are not necessary; most won’t help you get your foot in the door.
A good personality goes a long way. Nice models often get hired over more beautiful girls who aren’t as pleasant.
You need to be at least 5 feet 8 inches, slim (ideal measurements are 34-24-34), and preferably under 20.