1. Brush up your resume.
2. Apply to any and all psych facilities that you can.
2b. Apply for all positions: sometimes it's easier to get into a facility as a per-diem and them parlay it into full-time work, especially if you're switching specialties.
3. If you have a psych unit in your current facility, definitely apply for a transfer, or at least ask if you can shadow there.
To help if/when you do land an interview:
4. Start doing some psych CEUs. You can find a lot of them online for free/low-cost.
5. Get your hands on some psych nursing journals and start reading them. These are not as easy to find for free/low-cost. Some of the CEU sites may offer free copies of the psych nursing journal articles. Otherwise, try your local public library or even your nursing school library if you still have access to it.
6. And get out the old textbooks, or go to your local library, and do a bit of brushing up on psych.
7. Don't sell your ER experience short because it can be rather helpful when applying to work in psych. I'm sure you've seen a fair number of ER patients presenting with psychiatric issues, so it's not as though you haven't had any experience with psych patients.
8. If you are really serious about psych, consider joining professional organizations (APNA) and/or volunteering with a mental health organization.
Best of luck!