Depends on the niche. If it's not very competitive and you have already hit #1 you can get by with fresh content, social shares, and maybe a new quality link here and there just to be safe. I've had sites sit in the top 5 for 12+ months with no external link maintenance aside from the previous sentence if the competition is weak.
If other people are actively competing for the term then it's a different story.
Keep creating backlinks in drip feed and focus on social media too. Since if you will stop creating backlinks then it will make tasks easier for your competitors, as he can easily outrank you by creating more backlinksor just stop? If I am already 1st rank for these keywords is there any reason to build additional links for these keywords?