Start with a project you use or depend on in your own projects. It's probably best to start by enhancing or adding a feature on that project. Other things to l

Start with a project you use or depend on in your own projects. It's probably best to start by enhancing or adding a feature on that project. Other things to look for is a project that is managed by people who a receptive to pull requests and have accepted them routinely. Also look for projects that have lot of issues open and closing on a routine basis--this will mean the project is in active development. This will keep you motivated and provide you with some good mentors who may accept or suggest improvements to your pull requests. Along the way you will probably learn about forking repos, writing good commits, sending pull requests and most of all, contributing code. More mature projects have a lot of tooling such as running unit tests, adhering to coding standards, etc which can create hurdles to entry bfor beginners but if you do venture forth with these you'll develop some great habits.