The most useful tip I could give you (if you're building on rails and deploying to heroku) is to use a Unicorn Webserver. It allows your to handle far more concurrent requests.

This article explains it better than I ever will.

http://blog.codeship.io/2012/05/06/Unicorn-on-Heroku.html

I'm running 8 unicorn workers per dyno at the moment and that's still within the 512mb memory limit because I'm not using ActiveRecord.