I'd say the language in the button makes the biggest difference. So many email CTA's say "Take This Survey" or something. Instead, make your most important question the call to action button. So instead of asking them to take a survey, ask them to rate the service. "What did you think of XYZ Product?" and then your buttons are "Good" or "Bad" or whatever rating scale you want.
If your selling an eCommerce product, maybe the call to action illustrates the benefit of the product. So, if your selling scorpion repellent (yep, I said scorpion repellent), don't say "Buy Now", say "Get Scorpions Out of My House!". Especially if your email is simple and your landing page has more benefits for the member than your email, this could work wonders.