I would say the most important thing is to make sure that you'll be as engaged as possible with the DM and the players, and that the focus should be on having a great group experience! For the game itself, having a basic idea of what type of character you'd like to play is always helpful. Do you imagine your character as a fighter, spell caster, holy warrior, etc. You don't need to have a fully fleshed out backstory, but having a basic one helps in the roleplay experience!