Brittany Sudlow

^Agree. For more tactial tips: LinkedIn has some great overview courses on Product Marketing that is included with LI Premium. There are also local meetup.com groups that are worth checking out. Building a network and conducting informational interviews is always helpful and good practice for customer interviews you'll conduct as a PMM. For practice or even a makeshift "portfolio" you could take a current company and build out a fake GTM plan or updated messaging for the site. Presenting this in an interview with an explanation/reasoning behind your changes can show others how you think like a product marketer.

If you want any kind of quantitative data, purchasing a tool is really the only way to achieve that. I recently evaluated all the sales enablment options and went with DocSend. You can track any content engagement to accounts in SalesForce which you can tie to eventual Closed Won and Closed Lost to track true ROI. I agree with the above comments for qualitative evaluation. It's all about building good relationships with sales so they will be transparent and candid about what works and doesn't work...with useful feedback.