Ask first. Brief them well.

People who saw your work closely and recently, in work relevant to the new role — ideally a direct manager, plus perhaps a close colleague or client. Closeness matters more than seniority: someone who worked with you every week will be far more specific than an executive you met twice. Friends and family generally aren't appropriate.

Remind them when and how you worked together, say what role you're applying for, ask clearly, and include a genuine easy out — something like "if you don't feel you can give a strong reference, or don't have time, that's completely fine." It's polite, and it protects you from a lukewarm reference. If you haven't spoken in years, reconnect warmly first.

You can remind them, not script them. A short briefing with the role, what it needs, and two or three projects they saw — with results — helps them be specific. If a referee asks you to draft something, that's fine as long as they review it, change it as they see fit, and send it from their own account. Never send anything in their name.

Use another senior colleague from the same place, a client, a professor or tutor, a volunteer coordinator, or someone from a project. HR can usually confirm your dates and title even when your manager has moved on. Note that some organisations only confirm dates and title as policy, so it's worth asking a referee what they're able to say.

Nobody can promise how a referee will respond, and employers ask for different numbers — often two or three. What reliably helps: choosing people who saw your work, asking permission with an easy out, briefing them, warning them before the call, and thanking them afterwards.