Getting Started

Make sure you have a GitHub account.
Find the repository that is relevant to what you want to contribute.
Create an issue in that repository, assuming one does not already exist.
Clearly describe the issue including steps to reproduce when it is a bug.
If it is a bug make sure you tell us what version you have encountered this bug on.
Fork the repository on GitHub.

Making Changes

Create a feature branch from where you want to base the work.
This is usually the develop branch since we never do any work off our master branch. The master is always our latest stable release.
Only target release branches if you are certain the fix must be on that branch.
To quickly create a feature branch based on develop; git branch fix/develop/my_contribution then checkout the new branch with git checkout fix/develop/my_contribution. Avoid working directly on the develop branch.
Make commits of logical units.
Check for unnecessary whitespace with git diff --check before committing.
Make sure the commit messages are in the proper format.
Make sure you have added the necessary tests for the changes.
Run build.bat in the root to assure nothing else was accidentally broken.
We have a ReSharper layer that applies our coding standards so make sure that you're "all green in ReSharper"