Evaluating relative importance of Bible teachings

In the ESV Study Bible, there is an interesting overview of Bible doctrine by Erik Thoennes. In this article, he has a short statement on discerning the relative importance of theological issues. Thoennes groups these into four categories:

(1) absolutes define the core beliefs of the Christian faith;
(2) convictions, while not core beliefs, may have significant impact on the health and effectiveness of the church;
(3) opinions are less-clear issues that generally are not worth dividing over; and
(4) questions are currently unsettled issues. These categories can be best visualized as concentric circles, similar to those on a dart board, with the absolutes as the “bull's-eye”

But how do you decide which is which? Isn't everything important? What should we be prepared to give ground on? What really matters? What is worth standing for?

Phoennes gives some guidance here:

Where an issue falls within these categories should be determined by weighing the cumulative force of at least seven considerations:
(1) biblical clarity;
(2) relevance to the character of God;
(3) relevance to the essence of the gospel;
(4) biblical frequency and significance (how often in Scripture it is taught, and what weight Scripture places upon it);
(5) effect on other doctrines;
(6) consensus among Christians (past and present); and
(7) effect on personal and church life.
These criteria for determining the importance of particular beliefs must be considered in light of their cumulative weight regarding the doctrine being considered. For instance, just the fact that a doctrine may go against the general consensus among believers (see item 6) does not necessarily mean it is wrong, although that might add some weight to the argument against it. All the categories should be considered collectively in determining how important an issue is to the Christian faith. The ability to rightly discern the difference between core doctrines and legitimately disputable matters will keep the church from either compromising important truth or needlessly dividing over peripheral issues.

I appreciate these guidelines, but they still leave me wondering how you know what is less important, and whether it is acceptable to compromise over the lesser issues.