Removing Left Recursion from Context-Free Grammars - Ordering of nonterminals
This is actually not very complicated.  I'll assume that epsilon productions have already been eliminated from the language, because that will only obscure the key concept of "left corner".

Form a graph G where the vertices are all the non-terminals of the grammar.  Now draw a directed edge from A to B if there is any production rule that looks like "A -> B[...]".  The paper calls B a "direct left corner" of A.  More generally, some other non-terminal C is called a "left corner" of A if there is some path from A to C along the edges of this graph.  This can be done by computing the transitive closure of G, call it H.

The paper suggests ordering the vertices by counting the number of left corners each vertex A has (i.e. how many other non-terminals you can reach from A, or the out-degree of A in the graph H), then sorting them in decreasing order by this number.

One handwavy motivation for this policy is that if there is an important non-terminal (say the starting symbol S) with connections to many other symbols), then it makes sense to purge left-recursion from S early on, because if you leave it till later there will be more copies of S that you need to expand out.  I think the explanation in the paper is more convincing, but perhaps less obvious.