How to promote your software projects efficiently?

Put it on developer platforms and share it on Social Media
If you have an open source project, get yourself on services like GitHub and Open Hub. Be creative and get an entry on all well-known developer platforms. Put the website in your signature of forums, and remember don’t spam.
Here are some recommended social media platforms: Facebook, Twitter, Linkedin, Reddit, Dev.to, Lobsters, Hacker News, Product Hunt, Beta page, Human Coders.

Make your projects easy to use
Do you like software that is difficult to use and install? No way, because that would waste time. But, in most cases, you'll need to read the documentation and install it locally according to the prompts, which often takes a few dozen minutes or even more time. If It's very difficult to read, or missing some key information, it may waste a lot of time and fail to install. So my suggestion would be to test your software from the beginning, and take user experience into consideration.

Advanced usage of the tool
Visitors will want to know what your project is for, how it works, and how to use it right away. The common practice is to provide a demonstrating GIF or video demo. More importantly, you can also use development tools like Tin, so that other people can try your projects with one click.

Create clean and well structured documentation
Creating a good documentation is probably the most important step. If you have a small documentation, you can include it within your README. Otherwise, you should probably host it in a separate website. Some open source projects like vuepress can help you creating clean documentation in a simple way.

Keep your projects up-to-date
People don’t like to use outdated projects. A project that was updated more than 1 year ago, will lose new users. It shows that it is not maintained. Determine a release schedule in advance and update your projects and user manuals accordingly. Try to regularly release new versions of your project. Show people that the software is maintained and be careful with the usage of dates.