Depending on what kind of person you are, a different strategy would be in order, i.e if you tend to like being thrown in the deep-end try tackling the biggest github open issue you think you can handle.
If your the type to ease into things, find good-first-issues of projects you like:
<self-plug> checkout, feel free to reach out! :)
https://github.com/nabaz-io/nabaz/issues/2