Synonyms for Run-of-the-mill:

adj.

average (adjective)
conventional, average, routine, middling, medium, mean, mid, undistinguished, garden-variety, customary, midmost, everyday, mezzo, predominant, moderate, middle-of-the-road, normal, halfway, usual, common, unexceptional, mediocre, commonplace, stock, standard, median, stereotype, dominant, ordinary.
unexceptional (adjective)
unexceptional.
unoriginal (adjective)
conventional.

n.

nondescript, mundane. garden, garden-variety, undistinguished, routine, plain, unremarkable, indifferent, cut-and-dried, formulaic, good. run-of-the-mill (noun)
ordinary, unexceptional, run-of-the-mine.

Other synonyms:

unremarkable, garden-variety, formulaic, cut-and-dried. undistinguished, garden. indifferent. plain.