"Do one's bit"

                                                          "I do my bit"

            "I do my bit" = pongo mi granito de arena
                                   =  (informal) make a useful contribution to an effort or cause
                                   Ex. 'I was persuaded to do my bit for the environment"
                                   Synonyms: assist, help, lend a hand, give one's support, contribute.
                                                                                                 (Source: Oxford Dictionaries)

Thanks for learning with me.
:)