Start with a hypothesis
Write the question before the production brief. For a wellness app, it could be whether people respond to a calmer routine or a more measurable goal. For a game, it could be whether progression or competition is the stronger motivation.
Change one meaningful idea
When the hook, format and offer all change at once, it becomes difficult to explain the result. Use variations that isolate a useful creative idea while keeping the rest of the experience coherent.
Keep a learning library
Record what you tested, the audience, the context and the result. A disappointing ad can still teach you something; a winning ad is more useful when you understand why it might have worked.