The category you posted in Real Estate Virtual Assistants
has addressed this question and can offer some great advice.
I also suggest you take a look at this thread. It has exactly what you are looking for. Working with a Realtor Advice
You will find that agents want either specific admin tasks much the same that any small business owner wants completed...help with social media, blogging, website updates, etc. And/or they want help with their listings, showings, appointment setting, transaction coordination and experience in MLS websites.
You can still target RE agents for the specialties you do have but some will want experience in the programs they use to market homes.
I think you need to itemize exactly what it is you do best and then see if those skills are applicable to the businesses you want to target. Also, you will want to have a website up which reflects the message you want to send to real estate agents. You want to go where they go so do check out all the real estate sites such as Trulia, Realtor.com and Zillow.com. You can also see what's going on in the real estate world by reading and learning about the current market. Try Active Rain http://activerain.com/
Some states do require a license to perform certain tasks so you will want to research your state's requirements for assistants. Do check the VAF forum link I provided. I believe that information is listed there as well.