Most of the important points have already been raised by others (version control, CI/CD, etc.).

I would only like to recommend one specific tool, which you can integrate into your CI/CD pipeline: SonarCloud (https://sonarcloud.io/about)

The on-prem version is called SonarQube (https://www.sonarqube.org/) which you can easily host yourself if you need/want to, but the cloud version is dirt cheap.

This single tool can bring tremendous value into your work life, especially if you have a team full of junior/inexperienced people. It has saved me countless hours on different projects by providing actionable insights on their code bases.

Disclaimer: I have no ties to the company making SonarQube, I am just really thankful that this tool exists. :)