Select a commentary appropriate for your subject and area of focus.
Prefer commentaries with multiple authors. Ensure the authors are suitably qualified.
Reject commentaries which lack proper referencing and extensive bibliographies.
The best commentaries examine Scripture in context, not verse by verse.
Read the passage thoroughly, several times. Keep an open mind; your current understanding might be wrong.
Consult at least three different commentaries.
Beware of theological bias; your own as well as the commentators'. Reach your conclusion objectively.
The best interpretation is the one most consistent with the evidence.