Set your priorities and choose main keywords. You can't rank high for everything.
1. Interlink your posts. Focus on increasing strength of categories as they will help individual posts.
2. Review your post titles that improve SEO title and meta description.
3. Increase the number of articles. Example - news site can add subdomains with new niches - health.news.com, finance.news.com, cars.news.com etc.
4. Sponsor charity foundations or offer scholarship and get links from charities and universities.
Etc.