Jessica,
Welcome

and congratulations on your first clients. Are you interested in working locally or strictly non-locallly? I have local clients but focus the majority of my marketing non-locally. My local clients I still do from my office, there is just some other things they expect since I'm right here.
Let me know where you want to focus and I can give you some tips and ideas. Plus read the marketing forum that Tess mentioned, you'll get lots of tips there.
One thing with having bookkeeping as your niche is preparing ahead of time with how you will share documents and files. There are a couple recent threads in this area that discuss that. Have you already determined how to do the file sharing?
Good luck!