If you search for "press release writer" on Google I am on the first page - The Press Release Site is my site.
Here's what I did:
I used a wordpress blog as a website. I paid someone to SEO it for me. I personally have had great luck with wordpress blogs and SEO.
I regularly wrote blog posts about how to write press releases, how to conduct an online publicity campaign, how to SEO your press release, what to avoid when writing a press release, etc. I tweeted links to those blog posts on Twitter, Facebook, and Linkedin. Giving away free, genuinely useful information is my number one tip for getting people to link to your site. Especially if you post lists of links to useful sites on YOUR site - people love lists of resources.
I used to post on here a lot, and I had a link to my site in my signature line on here, which I think is good for SEO.
I am now regularly getting press release clients who found me on Google by searching for the term "press release writer". Oh, that's another thing - I sprinkled the phrase "press release writer" liberally throughout my website/blog.
If anyone else has any ideas as to how I ranked this well, I'm all ears.