I would start with speaking to any nursing professors you have a good relationship with and who you earned good grades with. You'll need references/recommendations.
At the ED you'll be volunteering at, bust your butt and make a great impression. Think of your volunteering time as an extended job interview
. Once you get to know more people, ask some nurses whom you trust about how they got hired and what their thoughts and recommendations are for how you can better prepare yourself to be a good fit for the unit. These are some of your best allies in getting hired if they think you'll be a good addition to the crew, especially since a lot of work places are starting to include peer interviews as part of the hiring process. Their recommendation also carries a lot of weight if they go to the higher ups to say they think you should be hired.
Also, once people get to know you through your volunteer work, you could talk to the charge nurse/supervisor/manager about how you're really enjoying volunteering at the unit, you'd love to work there for X, Y, and Z reasons, and you think you'd be a good candidate for A, B, and C reasons. Ask if there are any job openings coming up and what their usual hiring procedure is.