Forms are the top of a Klaviyo program: they capture the subscriber and the consent that everything downstream depends on, and they often feed a welcome flow. Their design and targeting decide subscriber growth and the quality of the data captured.

In practice

Capture consent cleanly at the form and pass useful data, such as a preference or source, along with it. A form that only grabs an email misses the chance to collect the zero-party data that makes the first messages relevant. Check the consent language, the list it submits to, and any hidden properties before launch, because a form that captures the right email but the wrong consent creates deliverability and compliance problems downstream.