First, you need to be able to look at your opt-in rate. Then ideally, see if you can figure out a conversion rate on that pop up as well.
(This is where a fancier pop up builder can be helpful since it will tell you what the conversion or acceptance rate is.)
With some data at hand, go ahead and test different offers. The most successful opt-ins we do start with a micro commitment. “Hey, would you like to save 10% off today?” Yes or no. If you can get them to say yes, then you ask them for their email. That tends to have a significantly higher opt in rate. Some of our clients doing this now are seeing opt-in rates of 10%, which is excellent.
The other thing to consider is the quality of traffic or the opt-ins. Sometimes you’ll see a spin to win type of sign up. Those will often have high opt-in rates, but the quality of the email is not as good. It could be a fake email looking for something free or they just aren’t as engaged.
Pro tip: Have a strong welcome series to accompany your opt-in. This is the flow that makes the money. If you give a deadline to the coupon you offer initially, you're creating that urgency and creating an opportunity to engage them in additional email by reminding them of the deadline. During this time you're also telling your story and you're introducing them to the brand, the team, the product and why they should buy.