At heart lament tedious decrees that are pretty bog-standard (8)
I believe the answer is:
mediocre
'standard' is the definition.
(thesaurus)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for mediocre that I've seen before include "Of middling quality" , "Second-rate, undistinguished" , "Ordinary" , "poor to middling" , "Of only average quality" .)