There are so many students are earning by doing part-time jobs in big cities like New York, Los Angeles in USA and London, Birmingham in UK. Some times it may not be enough to support your life and Education there .Therefore before going there, students must have enough funds to study there which they must show while applying for admission and visa.
Most of the coutries allow students to do 20 hours of part-time work while studying. But it is full time during vacations. Working 20 hours a week doesn't disturb in studies much. Instead they'll be experienced and know the life better. If a job done is related to subject being studied, students will have advantage to better understand their subjects and will also have opportunities to apply what they've been taught.