Becoming staff of a large community can be daunting, facing you against unknowns. Please don't over-think the role, as you will learn everything you need, on the job, in order to become a competent member of staff.
As a member of staff you will learn forum policies, know them well, and reference them as necessary before making decisions. Everything you do is about forum policy, combined with common-sense. When in doubt, ask first, act second. Experience brings competence. A good attitude and stable approach help immensely. We joke about the need for teflon coating, albeit you do need a teflon attitude.
Staff should never try to be all things to members, as you set yourself up for failure. Your role is to moderate the community to work harmoniously, not breakdown due to over-performing. Staff are not members shoulder to cry upon, they are not an authority on every subject, they do not try and respond to every thread under their control, nor try and solve the worlds problems. These are all failures in the making. Staff members are not God like, so please don't try to be.
As a member of staff, we use your strengths, and that is what you should focus upon and use in your role. Collectively, all staff bring unique attributes and knowledge to the staff community, allowing us to run as a team, not as individuals.
Staff should always remember what type of community this is, being mental health. There are members who may have serious diagnoses which can cause chaos. Staff need to be aware of new members befriending them after becoming staff, and ensure members do not unduly manipulate favouritism.
Staff must act unbiasedly at all times, be honest in all staff and member interaction, as these are the focal points for essential staff member communication.
Staff must always keep staff duties private from friendship interactions. History has dictated that some friendships will attempt to manipulate a staff member, influence them, converse about staff matters, and even collude with other staff outside the staff area, all of which will cause immediate termination of your position. When in doubt, ask first, act second.
Relax, breathe, and remember that being a member of staff is actually quite a rewarding experience. You help manage a community that change member lives forever.