Q:

A word meaning 'conforming to principles, hence effective'

Do we have a word that means 'effective/promising due to its conformity to principles [established in a given field of activity, etc]? An example context could be:

There remain a number of pressing questions, demanding [?] decisions.

A:

I think competent  comes close to what you are looking for: (from TFD) 

properly or sufficiently qualified:  a competent speech. 
suitable or sufficient for the purpose: a competent answer.

Competence:

The state or quality of being adequately or well qualified;

There remain a number of pressing questions, demanding competent  decisions.

