The first thing you should do is to remove all MODs, this will keep queries at a minimum.
Beyond using no MODs, what else can be done? Are there 'non-essential' queries that plain phpBB runs, which could be safely removed (and if so, how?)?
Since I'm asking questions... perhaps you can shed some light on this one... is there a good way to gauge how many queries per page barebones phpBB 2.0.4 is executing, out-of-the-box? I would love to get some hard statistics on what my board is actually doing to my host's mysql server.