Agents are definitely a good thing to aim for but are
very difficult to sign with. Your portfolio needs to be up to par, if not better than the other artists in the agency. Look at the artist's books in agencies such as Jed Root, Celestine, Cloutier, Artists by Timothy Priano etc.. to get an idea of the kind of work you need in your book. Even with a bangin' portfolio, most agencies are not signing much now-a-days. Work is slow within the industry so they need to focus more on getting their roster artists work, rather than signing more artists.
When signed, the jobs you may get will most likely be higher profile clients but you still need to keep promoting yourself and getting your own jobs. You need to be marketable for them in order for the partnership to work.
If you feel like your book is on the same level as the other artists, call the agency you are interested in and set up an appointment to talk to a booker and show your portfolio. Agents do not contact you, you practically need to beat down their doors to even been seen.
Having an agent can help you a lot but you need to be pretty established to even be signed in the first place. They are definitely not a "must have." Many artists choose not to take the agency route and do fine without one. Also, they take 15-20% of your payment.
Hope this helps!
