That will depend on how you can contribute to any given project. In order to do that, first thing would be is to read the documentation of any given project, where project owner will describe how and what type of contribution is welcomed. Don’t forget that you can help out in so many other ways beside direct code interaction, like localization, wikis etc.
Another way would be to work on your project all together. I’ve been working on React Native project. At a certain point I needed a charting/graph library that I can use. So, after a while, i found one. I installed it and started using it. Then, I saw that it’s missing certain stuff that I would need, so I started asking questions on github, and reading the original code of the library (which was java and i dont really know java). So, after a while I found what I need to do and started by basic copy/paste on certain library code. Everything worked and I sent a pull request to the author.
So, to sum up. Sometimes you don’t really have to start and search for the projects to collaborate and you can work on your own stuff. It might lead you to project collaboration either of the plugins you will be using or even better, someone would want to collaborate with you on your own project.