。
Listen to me carefully.
Literal
I [of-の] say thing [object-を] well listen-[give-くれ].
言うこと ('things [I] say, what [I] say') uses こと to nominalize the relative clause 僕の言う. よく ('well, carefully') modifies 聞く — here in the careful-listening sense, not the 'often' sense. ~てくれ is the casual masculine 'do for me.' A paternal or authoritative exhortation.