In the little time I have spent reviewing and discussing this subject, there seems to be a tendency for each party to talk past the other when referencing who or what "God" is. Obviously, different views of Trinitarianism and monotheism define "God" in different ways. Instead of focusing on areas of agreement first, however, each side focuses on what relevant heresy with which to label the other due to his or her different definition of "God." I think establishing common ground first is a viable alternative, at least if there is any - a denial of sola scriptura, for instance, would logically take precedence to this sort of discussion.
In any case, the sort of common ground to which I refer is the specific methodology by which it can be verified whose definition of "God" takes primacy. A word may, of course, have more than one meaning, but is there a proper or common usage? If such an argument is to be made, it should be kept in mind that Scripture rather than modern (or ancient) trends is the source material which one ought to appeal to as his justification; supposing the majority of professing Trinitarian monotheists may have one conception of "God," that would not imply theirs is the meaning the authors of Scripture most often associated with the word. Separating preconceptions from our examination of the pertinent Scriptural data is necessary.
But in the context of this debate, it should be easy to do this. Given that the discussions which this post is primarily written to facilitate have to do with disagreements about whether "God" refers to a divine person or to one [set of] attribute[s], first impressions would suggest that it shouldn't be very hard to look at a given passage and make the right conclusion. I fully admit I could be wrong, as a text can be clear, agreed to as the source for the resolution of a dispute, and nevertheless not yield agreement. Still, it's a simple enough idea.
Further, any self-professing Trinitarian monotheist should wish to avoid the charge of tritheism, where "tritheism" is understood as mutually exclusive with "monotheism." Both sides agree that there is one God, differing on who or what God is. So it seems to me that the most efficient course is for all sides to agree that the main meaning of "God" is whatever is most often (if not always) associated with monotheistic passages. For all the emphasis Scripture places on monotheism, I believe that is a natural assumption. Really, the only reason I can think of that one would oppose this is knowledge that the outcome would be unfavorable to his view. For the undecided, however, it may be useful. Collect all passages relevant to monotheism, determine with help from the context the meaning of "God" in each, and you have your answer as to the "proper" definition.