Your ad's only job is to get the click
Your ad gets the click, and your landing page gets the sale. Keep this in mind when you're designing creatives. Your creative only has two jobs: attract the right audience, and get them interested enough to click and come to your landing page.
Don't overstuff your creative with information
From the click onward, your landing page is going to get the sale. So when you're designing creatives, don't overstuff them with information. Don't explain your offer in full. Don't put every single detail you think is important into the ad.
Ask one question when designing a creative
Who am I speaking to, and are they interested enough to come to my page? That's it. Your landing page will do the rest.