Volunteer board members' motivation is service to the community. Board members are also community leaders and influential in the community, prime qualities for an advocate. Your advocacy efforts will generally be part of a planned board effort. Remember, you cannot speak for the full board, but you can speak about the board's position on issues. You can also promote the interests of the library at any time.
Board members are also advocates for the community to the library.
You represent community standards and interests and understand community needs. You should be ready to voice those community needs in board meetings, always cautious to represent the whole community and not just special interests. In addition to community influence, board members often bring personal expertise to the library board. Libraries never have enough money to hire all the expertise they need, so it's a natural for board members to offer their expertise to the library. That expertise could be anything from financial to construction, public relations to computers.