Which technique should be used to keep up the high-ranked keyword?

I have my keyword ranking from 8th to 2nd right now. Since SEO is a continuous process, what should I do now to make it stable higher for long?

Here are the techniques which will keep up the high ranked keyword -

1. Use on-page and off-page optimization techniques
2. Always remember contents are king so make sure you have the quality contents with proper use of the keywords.
3. Your website should be responsive.
4. There should be proper use of the tags, meta description, title tag, heading, images.

Find baseline ranking. Before doing anything else, find out where your page ranks today for the keywords you want to improve. Without a baseline, you will not be able to measure progress. You can do it manually (i.e., search for your keyword in Google and take note of your position) or use a rank-tracking.

Hi

Focus on Long-Tail Keyword Rankings
Group and organize keywords
Useful, high quality, relevant content
Page load speed
Image optimization
Header tags
Outbound links
Site architecture and navigation

https://www.welllivingshop.com/mattress-toppers/

SEO techniques such as internal linking in the form of anchor text, Blogging, Article submission, Forum posts, Website content.