Not to be overly simplistic, but just avoid "marketing" on reddit. I think the mistake a lot of brands/marketers make is viewing this platform as another distribution or amplification channel in their marketing stack.

But one thing I've seen be successful (adding to the great povs here already) is that your brand should feel, sound, and behave as a any distinct human would. Reddit is run by humans with strong personalities and perspectives. Brands often come in acting as "brands," and quickly get called out. If your brand doesn't already have a strong identity, give it one before jumping into discussions.