しない方がいい

had better not; it is better not to do (something)

→ 為る
phrase Rare #22,490
had better not; it is better not to do (something) Used to advise against doing something. しない is the negative form of する, and 方がいい literally means “the better option is.” It is commonly used in informal advice; add です or ですよ for a more polite or emphatic tone.
JA: それはしない方がいい。
EN: You’d better not do that.

結婚したくないならしない方がいい

If you don't want to get married, it's better not to.

これについては知ろうとしない方がいい

You’re better off not trying to find out about this.

— アトランティス 失われた帝国 (2001)

それはしない方がいいと思います

I don't think you should do that.

なんでこれしない方がいい

Why shouldn't I do this?

結婚したくないなら結婚しない方がいい

If you don't want to get married, you shouldn't.

この文はたぶん翻訳しない方がいいという気がします

I have a feeling this is probably a sentence that shouldn't be translated.

それはしない方がいい

You’d better not do that.

だったら何もしない方がいい

In that case, you're better off doing nothing.

— ニュー・シネマ・パラダイス (1988)

今年の夏は外国に行けるとは期待しない方がいい

You shouldn't expect to be able to travel abroad this summer.