I would say that I am far from an expert in managing a server.
What are the best 1-3 tips with regrds to server security? E.g. Firewall, user access restriction, deny from?
Contrary to popular myth that managing a Linux Server is difficult, learning to manage your own installation of Linux is very easy. Not only that the operating system is free of cost. It comes with a free owners manual called world wide web.
Internet is best place to learn about Linux. It has tutorials and courseware for every one from Geekest of Geeks and a total newbie. This proves that gone are the days when Linux Server were only the domain of geeks....
Peep into Google you will come to know more than here...