to lend a hand

• 请人帮忙

  ask somebody for help

• 帮了大忙

  be of great help

• 帮忙帮到底

  help to the end

• 请你帮帮忙。

  Please would you help me out.

• 请你务必帮忙。

  Please lend me a hand.

• 请帮我最后一次忙。

  Please do me one last favour.

• 我能帮你什么忙呢?

  Can I give you a hand with anything?