How many advisory shares should I get?

My background: Was a c-level exec at a company that I was very early stage at. We exited for 700 million+, grew from 1 to 1000+ employees, raised 50 million+ in funding. I was already a millionaire from before, but I gained additional millions after the deal.

I've been advising a founder and helping him close a deal with my former company using the expertise I have and the insider knowledge I've built. The company has raised $20k at a 500k valuation when it was an idea. Since then they've made some revenue and partnerships but nothing significant. Founders have Duke and Northwestern graduate degrees and many years of experience.

I agreed to a monthly call/sit-down.

I'm asking for advisory shares and they want me on board, but I have no idea what's fair and makes sense.

Any good articles on this subject. Anyone out there who have advisory shares?