It would help to have a few written paragraphs explaining a few unwritten rules of the community.
Sounds dumb, doesn't it?
But online communities aren't the same as real communities. It's harder to pick up non-verbal clues. We rely solely on what's written down to figure out how to act in any situation. Newcomers are pretty susceptible to embarressing themselves in front of regulars, and they know it.
It helps to write down a few general tips. If members typically don't criticise each other's skill in that field – it helps to write that down. If members usually welcome newcomers – it helps to write that down. If members dont mention certain topics, ask certain questions or reveal certain pieces of information about themselves – write that down.
Don't write down everything. Newcomers need to pick up on much of the community culture themselves if they are to feel a part of the community. But a few guidelines to help them committing a community faux-paux and feel confident to begin participating. These tips might also renforice the member's own sense of community.