Run this list before you send a single paid visitor to a page.
One promise above the fold that matches the ad. One main action. Proof within the first scroll: reviews, numbers or recognisable names. A page that loads in under two seconds on a mid-range phone.
Then check the boring parts: form fields cut to the minimum, tracking firing on the thank-you step, and a clear next step after the click. Most leaks hide there.
Only after all of that is green do we turn the budget on.