This will be just a quick post pointing to this article that I found quite useful and which I will undoubtedly re-read in the future.
I found myself having to setup new server from scratch at least one or twice a year - and oftentimes I wonder if I have done enough securing them so having found an article like this is very handy.
Without futher ado, here it is: My first 10 minutes on a server primer for securing Ubuntu