Actively participate in the whole site - read and rate others hubs, leave comments, reply to comments on your hubs.
Make use of the forums - if only to pass the time in the Sandpit :)
Always aim to write the best hubs that you're capable of. Never plagiarize or reproduce the work of others (about the same I guess). If writing for pleasure make sure your hubs are info rich and engaging for the reader.
Equally if you're here to earn money - learn how to at least do the basics of SEO - search engine optimization, which is the founding principle of being successful as a writer online.
There's plenty of reading material - both on the site (written by HubPages) and from Hubbers.
Most of all enjoy yourself. It's a great site to be a member of and I'm sure you'll learn the ropes in no time at all :)