There is a wide range of work opportunities for magicians, but to make a good living you must either be a great marketer or have a good agent. If you don't market yourself effectively you won't be successful.
Many performers don't have the interest in marketing their own shows. They use an agent to book them and the agent takes a percentage of the performance fee. Some agents take their fee onto yours and others take some of yours, but either way, they make some and you make some.
How much should an agent make? It doesn't matter. If you are making what you need from a gig, it really doesn't matter how much the agent makes. Realistically, most make about 20%, but even as much as 100% is not uncommon in some markets.
To work with an agent, you need to find them and submit your materials. Finding an agent can be as simple as opening the phone book and looking for talent agencies and entertainment agencies. You can also Google them.
Agencies will want you to send them a headshot. That is a picture of your face and shoulders for promotional purposes. They will also want any promotional material you have and a video of your act.
A good agent will provide you with business cards and even posters and other materials to use. Always give clients and prospective clients the agent's contact information when working a gig they booked for you. To try to circumvent the agent and steal a client will get you "fired" real quick.
Additionally, if someone has contacted your agent and then contacts you to negotiate a lower fee by cutting out the agent - don't do it. Alwys send them back to your agent.
When your agent learns that you can be trusted he will work that much harder for you. In the long run you will make much more money. You will also establish yourself with the clientèle as a person of integrity.
Agents can be a great source of work, but always show up for your gigs, be sharp, professional and do a great job. Your future success depends on your current work habits.