How do I cut my resume down to one page?

Cut by relevance first, then tighten wording, then adjust layout. Work through these steps:

• Remove roles that are old or unrelated, or reduce them to one line each.
• Keep only the three to five strongest bullets for recent roles.
• Delete bullets that repeat the same skill or duty.
• Shorten your summary to two or three lines.
• Group skills on a few lines and drop basic ones such as email or internet browsing.
• Remove "References available on request" and personal details that add nothing.
• Finally, adjust margins and spacing slightly if needed.

Ask of every line: would the employer miss this if it were gone? If not, delete it. A focused one-page resume often reads stronger than a longer one.