Spend the first generation on diagnosis, not decoration. Use a short scene with one subject, one simple motion, a stable background, and no complex transition. If that fails, a longer prompt will usually make the cause harder to identify.
Run a small test sequence: baseline prompt, one motion adjustment, and one framing adjustment. Stop after three attempts and compare them side by side. This cap prevents the free allowance from disappearing into random prompt changes and gives you evidence about whether the model understands your direction.
Calculate the trial before starting: available video credits / credits per attempt = maximum attempts. Then reserve one attempt for a controlled retry. If the product does not disclose video cost until the generation screen, record that as an access limitation rather than calling the plan fully free.