The first step would be troubleshooting for the issues. Firstly, it is important to note if it is a new project or not. The next step would include analyzing relevant keywords for the website that has to be optimized along with studying competitive analysis.

There could be two cases:
The website and pages have been indexed and appeared in the first 10 pages of SERPs but not in the top three pages, so there it needs some transformation on page descriptions, page titles, page text etc. However, if the website is still not indexed or dropped from the index, it might comprise of some big issues and a total re-work might be required.