Persona Alignment: So there are a few things you can do for this page. First things first though, do you have the organizations customer personas? If so, do you know their search habits? What are they searching for? Performing a keyword analysis might help you refine and improve the copy that is currently on the website. This is always my number 1 go to before I start on any projects.
Competitor Analysis: Who are you competitors? Who is linking to them? What anchor text are they using? This should help you to come up with ideas for your own strategy.
Meta Tags: I took a very quick look at your source code and couldn't find any associated description. Definitely something you will want to add, especially from the usability side.
Link Building / Winning: It appears open site explorer doesn't have your site listed so I'm guessing it is pretty new. This will be a great resource for you though. Start looking at link building options though, are there local organizations who would want to provide this site as a resource? What kind of anchor text do you want to use?
Blogging: I know you are saying you are planning to add more content and that takes time, but blogging is an awesome way to start talking about popular topics around your keywords. Also, for a sobriety clinic such as this, I would say it would be worthwhile to establish yourself as an expert in the field.
Social: Engage socially, it looks like you have recently set up your social profiles, so use these to promote good quality blog content and engage with others in your industry
Local SEO: Use a tool like getlisted.org and make sure you have a local presence! If people are searching for rehab centers locally, they might not find you if you don't have a strong local presence.