If you didn't get along well with your former boss, ask someone else with whom you've worked for a reference - preferably someone with a managerial title.
If you know that a former employer had reservations about certain aspects of your work, tell her that you've improved in those areas. She might be willing to think again and give you a recommendation based on your strengths.
If you've never held a paid job, ask a former teacher or supervisor you worked with in a work placement or a voluntary unpaid job for a reference.
To avoid alienating a referee, always call first and ask if she would be willing to recommend you. Follow up with a thank-you note.
