First of all do a proper on-page audit of your website
Get rid of All the toxic and low quality backlinks and disavow the toxic ones
Fix all the Broken Link Issues. Do proper On-page and make sure that your Meta TItle, Description, Keywords, H1, Alt Text all are optimized properly.
Do proper Keyword targeting and placement and build links using the exact or phrase match anchor text
Do submission on High quality sites with High domain authority.
Guest Posting on High quality sites will certainly be helpful for you