Ahead of getting to the 30/60/90 day plan, what background have you see Jr. PMMs coming from that could make them most successful in the role?
I've honestly seen everything! I've seen folks come from Sales (as I did), from content marketing (typically great writers), from demand gen, from a finance background, from customer success. Someone coming from a sales background vs a finance background into PMM will definitely showcase different strengths/weaknesses (i.e.what will come more naturally to them vs requires more work)
But when hiring junior PMMs, I look less for the background and more for the skillsets I need.
Are they hungry to learn?
Are they curious? Do they ask good questions - or seem interested in how things work? Are they able to connect the dots and see how things come together?
Can they be customer facing? Could they interact with customers? And prospects (though less need for this at the junior level)?
Do they have good writing skills - doesn't have to be exceptional, but basic/good writing
Are they collaborative and team oriented? Can they work well with others?
Why do they want to transition into PMM? What excites them about the role?
Can they do research (competitive, product etc)?
Do they have project management skills? Are they organized? (THIS IS SOMETHING YOU CAN TEACH so I don't over emphasize it, but depending on what you will need them to do, this might be more important).
I try to focus on the intangibles (teamwork, drive/motivation, curiosity, culture fit etc) but of course you have to balance that with what you need for your business. Do you need someone that will require less coaching or you have the time for more intensive coaching? I've been in both scenarios and it definitely changes who I hire.