宁缺勿滥 is to prefer go without something rather than have something shabby, shoddy, or of low quality. You can make a comparison to the English expression: "quality is better than quantity" or "preferring quality over quantity"

宁缺毋滥=rather go without than have something shoddy /put quality before quantity for instance Rather go without than have something shoddy. Don't find a man unceremoniously, this would not be fair to you and him, and the lack of a sense of responsibility too.宁缺毋滥。不要因为寂寞随手抓一个男人，这对你和他都不公平，而且太缺乏责任感。

I prefer lack of something rather than have many useless things.