As an international student you have several options. We've listed just a few ideas below.
Student Union: get experience doing everything from barman, to managing societies to helping arrange events. This won't always be paid work, but it can provide useful experience and will be a useful way to meet new people.
Student Research Assistants: if your university is well-known for its research then you may have positions in departments to help with that research. If you are considering a career in academia this will be a helpful way for you to explore whether you do want that career.
Office work: this can be a wide range of tasks. Not all of them will be exciting. Getting into an office though gives you first-hand experience of what happens in the world of work.
Remember though, if you are not an EU citizen and are studying in the UK on a Tier 4 visa you will be limited to 20 hours per week of work. You can read more about in another of our forum posts.