Caroline Walthall
Director of Product Marketing at Quizlet | Formerly Udemy

Other than the things already mentioned throughout my answers (relationship building, offering to facilitate planning sessions, etc.), I would also try to show them your own marketing calendar/roadmap. 

Share what you think your goals will be and ask to compare it to the rough product roadmap. Start by asking questions and sparking discussion. As you gain rapport and trust with your product teammates, they'll be more likely to bring you in at early stages, knowing that you are there to be a partner rather than an antagonist.

Eileen Buenviaje Reyes
VP, Product and Growth Marketing at 1Password | Formerly Dropbox, SurveyMonkey, LinkedIn
First off, don’t expect it to happen quickly or by brute force. Gaining influence requires trust which can only be built over time. Start with a few small wins to establish credibility. For example, market or customer insights presented at the right time in the product development cycle can be hu...more
Daniel Waas
VP Product Marketing at AppFolio
See my answer to a similar question on this page. You'll need to build trust and rapport with them and you do this by knowing your stuff, bringing unique insights, and having a well thought out perspective on key industry challenges. You keep overdelivering until your PM counterparts understand t...more
Carlos González de Villaumbrosia
The real first question you should be asking yourself is how can you empathize with product. Just as with your role and other PMM roles, Product Managers and members of the product team are swamped with suggestions, demands, and interjections regarding how they should go about improving their pro...more
Josh Colter
Head of Marketing at Woven
Product is comprised of people. And so it should be clear upfront that you need to start with a foundation of trust with the people in product. Take them out to coffee. Ask about what motivates them personally. What do they want to accomplish? Who do they read/follow for inspiration and growth? ...more