There is a variety of options you could look at. This advice is assuming that you are based in the UK.
Hospital based involves working with people who are unwell and require a period of treatment and observation that cannot be achieved at home. A lot of psychiatric nurses start out on wards but move out to the community and become a Community Psychiatric Nurse who visit people in their own homes, administer medication, monitor mental health and offers support and advice.
The other options are work in the community such as a psychologist or social worker (which would prob require further training). A growing number of charities (voluntary sector providers) are winning tenders from local authorities to provide community services such as supported housing, registered care, resource centres,counselingg services, back to work schemes and community advocacy.
To be shortlisted for entry level work in mental health you normally have to have a minimum amount of experience such as volunteering or supporting a friend or family member who has mental health issues. To gain experience it is worth approaching your local volunteer bureau or mind association to find out what opportunities are available. It is also a good idea to be aware of what is happening and latest developments in the field. I am always impressed if when I am interviewing people who have a good (or at least basic) understanding of issues that matter to us such as user involvement, the recovery agenda, and an understanding of equal opportunities etc.
Good luck!