This is how I have it for an Octopress in Heroku:
In the config.yml fill in your url, title, subtitle, author, description
The rest of the defaults should work.
If you have a custom domain you have to add a CNAMe file.
To create a new post you use rake as in rake new_post['Name of awesome post']
Then open that post. It is under the folder source/_posts
Add contents after the yml header
Save file.
Then follow the steps of deployment.
I documented an octopress to heroku deployment on my blog here:
There is no mystery to it. If you have more questions tweet me @tomordonez or reply back with your results