Welcome campaigns are probably the most common and easy to implement. It is merely about sending an automatic email moments after the registration or subscription ends.
A welcome is always appreciated. It is an opportunity for you to introduce yourself to the user, to tell him what he will receive in the future by subscribing. You can also take advantage of this email to give you free content, something that will be necessary if you have used a lead magnet to generate those records.
Other things you can do in these emails is to enable a small form where you ask the user the topics that interest you most of the ones you deal with on your website, what types of products interest you most in your store … This way you can segment much better and automate the next mails, correcting in what interests that user.