Always think twice before agreeing to sign a contract without reading it.

think 的意思是"思考、考虑"，这里指做出决定前的思考过程。 twice 是副词，意思是"两次"，在短语中引申为"反复考虑"。 think twice 是一个固定短语，意思是"三思而后行"，强调在做决定前要慎重考虑。