To start - remember that no matter what you do, it won't be enough. Someone will still complain that you didn't send smoke signals as a communication method.
Speaking from a B2B context, I have found success with communicating in the following ways:
- Slack - as soon as features launch (or a heads up a week or so out) posting a nice update in a product channel. Make sure to mention and thank the team that made it happen because we, as PM's, don't actually build anything ;)
- Monthly meetings - in a monthly sales or customer success meeting, communicate all of the product updates that have launched or are launching before the next meeting. Make them feel prepared for inevitable questions. Demo it! List who they should contact with questions or articles that can help them if they get stuck. Record the meeting and share it!
- Email newsletter - after the said monthly meeting, send out a monthly newsletter with a roundup of everything that was discussed. Include a link to the recorded meeting as well. This helps those that couldn't attend the meeting.
- Monthly product training - Ensure you have a dedicated monthly meeting to train the GTM teams on the newly launched, or launching, features. Again, make them feel comfortable. Be sure they are engaged. +1 if you have a dedicated Product Trainer.
- Product Marketing docs - working with your product marketing teams, ensure they have everything they need to create the necessary collateral. They'll likely create one-pagers, slides, and other imagery that GTM teams can use to promote the new features.
These few bullets tend to cover most of your bases but there's always room for improvement.