In this NY Times piece, various experts advise college graduates unable to find jobs in their fields.
You do not want it to appear that you were idle during your time of unemployment.
Focus on "developing skills you need for employment and learning about your industry". Research, taking advantage of your college's alumni network to talk with people in your industry. Master relevant software, like Excel and PowerPoint. If you are volunteering or working at any job, focus on the skills that transfer to your desired career. Even the lowliest customer service jobs can provide training for a future professional track. (I can attest to this.)
Take advantage of social media for networking. For example, start tweeting or blogging about the latest research in your career interests. Polish up your LinkedIn profile.
Start a business, any business, either high-tech or low tech. Even a dog walking service can showcase your entrepreneurial bent.