The official subreddit for ads created using the self-serve platform is Reddit.com/r/selfserve. It's a community of self-serve advertisers. Ask any questions you have about Reddit ads, share results and your experience with Reddit ads. Learn from other advertisers, throw in your own advice, and ask admins anything about Reddit ads.
To discuss the sidebar banner ads on Reddit navigate to Reddit.com/r/ads
Reddit aims to foster a channel of communication between advertisers and the Reddit ads team. In order to keep the community up to date with what we are doing and provide insights on best practices, Reddit has created a newsletter which keeps advertisers up-to-date with relevant news and information! Users who subscribe to the newsletter will receive a monthly email with information about the latest updates on Reddit's advertising side.
You can sign up for the newsletter here.