3 sentences

1. 他做起事来一丝不苟。

   tā zuò qǐ shì lái yī​sī​bù​gǒu.

   He is meticulous in everything he does.

   Source: Dong Chinese Dictionary

2. 他坐得很端，神情专注，不苟言笑。

   tā zuò de hěn duān, shén​qíng zhuān​zhù, bù​gǒu​yán​xiào.

   He sat very upright, focused and serious.

   Source: Dong Chinese Dictionary

3. 他做事向来一丝不苟，从不出错。

   tā zuò​shì xiàng​lái yī​sī​bù​gǒu, cóng bù chū​cuò.

   He is always meticulous in his work and never makes mistakes.

   Source: Dong Chinese Dictionary