straight and narrow

the straight and narrow (path) (a straight and law-abiding route through life; the way of proper conduct and moral integrity) — праведный путь; стезя добродетели (ирон.); честная, праведная жизнь; добропорядочная жизнь
If you keep on the straight and narrow, you behave in a way that is honest and moral:

Example 1: The young man was back on the straight and narrow after his discussions with the police officer and social worker. (idiomconnection)

Example 2: You have to keep to the straight and narrow if you want to stay on her good side. — Тебе придется вести праведный образ жизни, чтобы быть у нее на хорошем счету.

Example 3: The threat of a good beating should keep him on the straight and narrow. (CALD)

Collocations:

to stay / keep on the straight and narrow (behave in a way that is honest and moral) — не сворачивать с пути истинного; не сбиваться с правильного пути;
to stray from the straight and narrow — сбиться с пути (истинного);
to quit the straight and narrow — стать на путь преступлений; пуститься во все тяжкие;
to return to /be back on the straight and narrow — вернуться к честной жизни

Cf.:
[toe the line]
[stay the course]
Opp.:
[пуститься во все тяжкие]