Not to be crass, but where we place our derrieres says more about us than we'd like. In school, if you wanted to be thought of as the quiet girl who sat in the back, you sat there—and, in effect, that's who you were. And if you wanted to be thought of as the head of the class, you sat right up front.
Is your book club or volunteer meeting that different? If you eventually want to be the one running things, plant yourself at a power end of the table (hint: there are two of them) and voice your opinions. If you want to coast by and just enjoy the group, without handing over half your life, sit over by wall. The nice thing about being a grown-up (and not in school), is that you have the life experience to understand what you want—and choose accordingly.