If you are completely new to the hobby it is perhaps easiest to email me (scaryfatmaniffer) via the website or ring me (Chris on 01754 811125) and have a chat first. However all you really need to do is have a basic look at the rulebook design a character that you will enjoy playing and that fits in with the ethos of Derarkshire - grab a simple costume and come along.
First time tavern nights are only a pound entrance (usually) so if you don't enjoy it's not a huge outlay.
Things to remember - you can design your character and develop a background as you go along - try to play something low key . Nobles and very powerful characters are usually played by the plot team and new characters are usually designed at about 400 experience points which allows everyone to start relatively equal in power.
People usually find that the characters that do well are played by people who are cunning and thoughtful in their character development and get involved with the plot.
Power comes as much from who and what you know as it does from who you are and how experienced you are.