How can I start contributing to Open Source Softwares?

I'm a Software Engineer student and want to start contributing to open source to improve my skills. I know how to use git, repositories and generally the development workflow as I always did with my own side projects, but I don't know how effectively start contributing to an open source project. I feel like I don't have the skills to contribute to large projects meantime I cannot find a small one that motivate me. Any advice? Thanks in advance