1. Find a project that you like that has something that you want to improve
2. Take a look at the repo, see how many people are contributing, who contributes the most, is there a roadmap and changelog and read it, are there release numbers or not, is there a guide for contributing, has someone already attempted to solve your issue?
3. Ask devs if it is a good first issue and guidance. File an issue if it is not already there, discuse it. If they use another plataform to discuse new features, ue that.
4. Clone the repo, compile the code before doing anything, and try to implement the feature / fix the bug
5. Look at the commit format of previous commits and use it. Group related changes to the same commit. Write informative commit messages. Make a pull request with all the necessary information about it.

Use common sense, don't be afraid of asking, don't be a dick.

Maybe the project you would like to contribute does not want help. Don't take it personally, either fork it and do your thing or search another project.

Don't forget that you can also contribute documentation or data in some projects (for instance OpenStreetMap)

fillde -> filled

Nice, that's a start. You can pick something you are interested in, for example your favorite OSM editing tool and try to improve it in some way.

Since I guess that you are interested in kbin too, you can try to improve something on it.