What is a low hanging marketing channel/hack/trick most entrepreneurs ignore?

Everyone talks about paid ads, and email funnels- but there are often simple, high-impact things sitting right under our noses that barely get attention. It could be something that costs almost nothing, scales surprisingly well, or just works because nobody else is doing it consistently.

I’ve seen businesses double their inbound leads just by tweaking one underused channel- but it’s rarely the same for everyone. So what’s a low-hanging marketing channel or trick most entrepreneurs ignore?