Best practice converting free plans to paid plans

Hi Hunters! We are running a SaaS platform called GoatSign (https://goatsign.io) and have a free plan. I am looking for best practice / experience from other SaaS startups on how to, in a structured and systematic way mature and convert free plan users to paid. What are your experience and advice - methods, tools, does/donts, etc. Hit me 🙏😊