Not all leads are "cold", but they also might not be ready to buy. While I think speed to lead is important, what you say can make or break your chances.
When I think of "soft inbound", the triggers that come to mind are typically related to marketing.
The prospect either attended an event, they downloaded an ebook... heck maybe they comment on a social post from you or the company.
These folks didn't ask to be engaged, but they're engaging with your brand.
So... how do you prospect them?
Simple: Start a conversation
"Hey, saw you were checking out our State of Outbound report."
"Usually, folks are looking for ways to improve their reply rates."