You may find it helpful to look at codes provided freely for books. Take a look at wrox.com, samspublishing.com, advancedlinuxprogramming.com.
There are also a lot about Linux low-level programming, available as HOWTOs, tutorials, or tips and tricks. Just make a Google search for one! (There are a lot available at tldp.org).
As you have gotten more familiar with C programming, it's a good idea to start looking at other ones open source application. It's kind of Hack! and is very interesting job. I love to do something with open source games

.
At last (I advice as a grand father), not to try to learn every thing (mostly different and without any conceptual relations) about something like Linux. It's good to know programming, but there is no need to waste your time, learning emacs short-keys. Try to write programs efficiently and more and more rapidly.
That’s all I think.
Whish it help.