Technique one: ranges. If a process took roughly three days and now takes roughly one, "reduced turnaround from ~3 days to ~1 day" is honest. The tilde marks the approximation and keeps the statement accurate.
Technique two: relative change. "Reduced support tickets by roughly a third" is measurable without being exact. Percentages and fractions are honest when the underlying change was real.
Technique three: observable outcomes. Some of the strongest resume lines do not have numbers at all. "The tool became the primary way the support team handled escalations" is an outcome that does not require a metric.
Technique four: scale. "Led weekly deployments for a service used by roughly 200 internal users" communicates size without a percentage. Scale is often as informative as improvement.
What to avoid: absolute numbers you cannot defend. If a recruiter asks you to explain a number and you cannot, the interview is effectively over. Accuracy beats precision every time.
When you do have real numbers, use them. "Increased revenue by $120,000 in the first year" is stronger than "increased revenue significantly". Numbers make the story concrete and concrete stories are memorable.
A useful rule of thumb: at least one quantified or observable outcome per role. Not every bullet needs a number, but every role should have at least one entry that tells the reader what the work produced.