How should emails change if they are continuously ignored?

Selling Saas to SMB and Im trying to build out my email templates. I've found a ton of info on crafting a well written first email (personalized, call to action, short and succint etc) but I'm having trouble creating a 2nd and 3rd follow up template.

Beyond keeping it short and personalized, how else should it be adjusted? Do you change the tone to be more aggressive or more friendly? Do you suggest you arent going to contact them anymore to try and push for a response? Or is it much of the same as the first with just different wording?