If you are looking to improve your portraiture skills before you start asking people to hand over their hard earned money for a session with you, one of the things you might want to consider is Model Mayhem.
It is possible to get models that are willing to trade their time for images to expand/improve their portfolio.
Before you go that route I would like to give you some suggestions to work by:
1. Be prepared. Don't bring a model in for a shoot until you have it well planned out. Both what you want to shoot and how you want to shoot it. I have heard horror stories (from models) about being brought in and have the photographer say "okay, pose!". I kid you not. A movie director would not say to an actor "okay, act!". Communication is key, a model can only give you what you are looking for if you (as the photographer) take them to that place.
2. Get the images back to your model in a timely fashion, they did their part and you need to do yours.
3. I encourage models to bring chaperones, I explain to them that going off to meet a stranger alone is not a smart thing to do.
4. Another thing I instruct them to do is to let someone know where they are going and when they expected back. The fact that I express concern for their safety helps put them at ease.
5. Have them bring their own music. Having something familiar will help them be more comfortable, less out of their environment.
6. Once the session is about to get going I tell the model they need to let me know if anything I ask them to do puts them in an uncomfortable position, either physically or intellectually.
7. It is not uncommon to have your model in the perfect pose and as you are about to snap the shutter you notice their collar is out of position or a piece of hair is in the wrong place, but you don't want the to move. Do NOT approach them to fix the issue without first telling them you will be approaching them and explaining what you are going to do.
8. If a model has had much of a drive to get to me I ALWAYS give them gas and toll money.
9. Should the shoot be longer than 4 hours I will also offer them lunch.
10. Though I have them sign a model release I always explain to them how and where I plan on using their images.
Those are (some of) the important rules that I go by.
Before you start using Model Mayhem you really need to head over to the Photographer & Model podcast, hosted by photographer Ron Davis and Model Shawna Rencher.
Each week you'll get a 15 to 20 minute interview, sometimes a photographer, sometimes a model, but both will give you their personal insight and perspective from a shoot.
An exerpt from their website that says (well) what it's all about:
"There are hundreds of photographers and models just like you working together to create stunning images. On the Photographer & Model podcast we interview those photographers and models so you can learn how to do the same. The show is about: Art, Relationship, Creative Process, Creativity, Diversity, Experience."
If you are looking to become a better photographer by learning how to manage, control, direct a portrait session/model shoot this is something you should seriously consider.