What's generally required to get referendums on state ballots?

I know this can vary by state, so I’m looking for the basics. So what’s generally required? Petitions? If so, is that it? Do state assemblies then have to approve them? I was pretty disappointed to see that there wasn’t much going on in Illinois as far as referendums go.

The Initiative & Referendum Institute has a lot of info on this.

Very informative, thanks…