Behaviour-wise, following the prompt, I've replaced checking Reddit with checking Hacker News (similar enough to work, without getting too engaged with the content). I've also replaced Twitter with curated Tweetdeck streams, and Facebook for the news feed with newspaper apps (a free one like AP could work, though I pay for newspaper subscriptions).
Cognitive-wise, in terms of thoughts, I also recognize that social media is designed to hijack your attention and maximize engagement, so I've chosen to frame it as a negative (versus a neutral) habit for my own personal goals.
In short, replacing the habits with similar ones with better consequences, and understanding why I'm doing this has helped.
If we're talking about how social media shortens our attention span then it may be prudent to reduce usage.