“Improve conversion” is an objective, not an experiment. To make it testable, choose a particular step in a journey, a reason it may be failing and one change that addresses that reason.
State the uncertainty
Write what you do not know. For example: “People may be abandoning this form because they do not understand why the telephone number is required.” That is a proposed explanation, not a finding. You may need interviews or a usability review before deciding what to test.
Change one understandable thing
A smaller change is easier to interpret. If you rewrite the headline, shorten the form and replace the price display at once, a result cannot tell you which part mattered. Sometimes a full redesign is necessary, but it should not be presented as a precise test of one sentence.
Illustrative experiment card
Hypothesis: Explaining the need for a telephone number will reduce avoidable form abandonment.
Change: Add a short explanation beside that field.
Observe: Completed valid submissions and the quality of the resulting enquiries.
Guardrail: Do not accept more unusable submissions as a success.
Decide how the result will be judged
Define the eligible audience, exposure period, primary outcome and conditions for stopping before reading the result. Where statistical comparison is appropriate, plan it with the actual baseline and available sample. Do not invent a universal minimum sample size or stop the test at the first attractive fluctuation.
Make room for an inconclusive answer
A small site may not receive enough observations to separate a modest change from normal variation. In that case, keep the uncertainty in the report. A qualitative improvement can still be worth making, but it should not be sold as a measured uplift.
Keep a change log
Record the version, dates, audience and any other campaign or product changes during the period. Write the next decision in the same record: retain, revise, investigate further or stop. An experiment archive is useful when it prevents the same uncertain idea from being tested again without new evidence.
Use the measurement note to separate actions from outcomes, and the content brief when the change involves a page.