From your experience, what are some best practices for product management and product marketing to work together effectively?

Good question. I view product management and product marketing as close partners since we co-own the strategy and business outcome. Cannot say I have best practices, rather some guiding principles of how I would like to see us work together.

1. Involve each other early. I hate the model where the product team does a hard handoff to product marketing only when the product/ feature is ready to launch. PM, PMM, as well as other disciplines like Design, Engineering, and Data Science all bring unique perspectives to problem solving. You are much better off involving each other early so that the PMM understands the “what”, “why”, and “when” of what is being built; and the PM knows how it is going to be marketed to target customers.
2. A healthy debate is a good thing! We all bring our unique experiences to the table and it’s natural to have different opinions. Cherish that and don’t be territorial. It’s OK if the PMM questions why you are prioritizing feature A over B in the roadmap. It’s also OK if you ask whether the marketing plan is going to achieve the awareness or acquisition goal for the product. For the teams I’ve been on, I’ve always felt open, respectable discussions and sometimes debates have led to better decisions.
3. Respect the other side’s expertise. At some point, you cannot continue to discuss/ debate and the team needs to move forward. That’s when you have to respect your partner’s expertise and “disagree and commit”. This is especially important to remember for people with strong opinions - myself included! :)

I always start with roles & responsibilities. What is it that PM will be chiefly responsible for versus PMM? Starting with Pragmatic Institute's framework and agreeing to who will lead each activity is a good way to kick this off. Overall, I do tend to think of PMM as PM's single route to market. It's on PM to do the research ("customer development") and work with engineering & design to build the right thing, including the right scope to be sufficiently valuable. Now assuming the product has product/solution fit, achieving go-to-market success is largely on PMM. That includes the ability of sales to sell it, the clarity of supporting materials like data sheets & the website, and clear positioning and messaging that underpins all of it.

At a smaller company, effective collaboration between PM & PMM is going to be based more on personalities rather than responsibilities, since everyone wears so many different hats in a startup. Nevertheless, having an informal conversation about who is going to do what, and checking in periodically on how it's going, will help avoid friction in the long run.