Managing GitHub Notifications
You can "Watch" or "Unwatch" any GitHub repository, meaning you will get notifications from ALL discussions. This is a good idea for a repository that you are doing a lot of work on.
Click at the top of a repository page to watch it. Go to https://github.com/watching to see what you are currently watching and unsubscribe from things you don't care about.
If you are given push access to a repository, you'll automatically watch it. You can turn this off by unchecking "Automatic Watching" at https://github.com/settings/notifications so you're not signed up to watch stuff just because you've been given access to the git repo.
You are automatically "subscribed" to any issue thread that you start, comment on, or that someone @mentions you in, even in unwatched repositories. This is useful but can get tedious if a conversation continues past your interest. You can unsubscribe from any of these threads by hitting the button on the right of that issue thread. You can do this as soon as you comment on an issue that you don't want to keep talking about.
Alternatively, you can filter your notifications at your e-mail client, instead. Both Gmail and Google Inbox have automated categories/bundles that filter GitHub notifications away from your primary mail, or you can set filters manually to filter notifications@github.com.
Those who manage e-mail through self-hosted/command line tools may be interested in Notmuch.
If you go this route, and you're a member of the SWC GitHub organization, you can filter mail from SWC repositories using "Custom Routing" under https://github.com/settings/notifications. This lets you direct notifications from the SWC organization to a custom email address. For Gmail, you can take advantage of the ability to add whatever you want to your email with a "+", and send SWC mail to your.name+swc@gmail.com for filtering.