Using your initiative is very much focused on making things happen and putting ideas into action. These ideas are unlikely to provide evidence of initiative in a written application, but they might be things you reference at interview.
Suggest activities to do with your group of friends, and make it happen. Don’t just be responsive.
Many of the ideas above can grow into long-term commitments. Focus on ideas or issues that are important or which give you a sense of accomplishment and energy, so that your sustain your commitment. For example:
Start a campaign about something you care about, and get others involved.
Start your own business or social enterprise.
Set up a society, journal or club.
Set up an Oxford student arm of a professional organisation or a charity.