godan verb (-ku)
Used when deciding not to do something, often because it's not necessary or to avoid trouble. Implies a deliberate choice to refrain.
今日は飲み会をやめておくよ。
I'll pass on the drinking party today.
It looks like rain, so let's skip going out.
godan verb (-ku)
cut it out; knock off; let it drop
Used when stopping an ongoing action or behavior, often abruptly or as a suggestion to quit. Can imply 'that's enough' or 'stop doing that'.
もう遅いから、今日の仕事はやめておきなよ。
It's late, so why don't you knock off work for today?
その話はやめておこう。
Let's drop that subject.