To be engaged in two occupations or roles at the same time; to juggle two jobs/commitments.
彼は教師と小説家、二足のわらじを履いている。
He works as a teacher and a novelist—he's wearing two pairs of sandals (i.e., has two jobs).
大学院生は研究とアルバイトで二足のわらじを履くことが多い。
Graduate students often juggle research and part-time jobs.
二足のわらじを履くには時間管理と優先順位が重要だ。
To hold two jobs at once, time management and prioritization are important.