You absolutely must test everything you do, and testing your squeeze page is no exception. You must have a method to test how different changes in your script create different opt-in rates to your list.
There are many different ways to do this, and they will depend somewhat on your existing software and programs.
If your auto responder service offers tracking, and especially if they have the ability to rotate the web form, then you can track the sign-up percentage via your auto responder. For example, one web form might offer a free book, while the other offers a coupon for 25% off the first order at your web site. Which offer gets the highest sign-up percentage? You might test two different headlines against each other. Which one gets the highest sign-up percentage? Test everything you do, and only test one change at a time. If you make three changes, and the response rate goes up, that is pretty useless information if you don’t know which element made the change occur.
Another way to do it is to create several different squeeze pages, each with one change on it. You subscribe to a web URL rotator service, and each of the different test pages will be viewed in succession by each successive visitor. When you run your advertising (or whatever you are doing to generate traffic) you will put in the rotator link rather than the squeeze page link. Each time someone clicks on the rotator link, the rotator will rotate to the next squeeze page. You can then compare sign-up rates between the different squeeze pages.