I have given a quick start on Unix Socket Programming. If you have gone through this tutorial carefully then I hope that you should be able to write your TCP/IP client and server programs very easily.
After completing this tutorial you should be able to implement simple protocols like SMTP, POP3 and FTP. Even when I learnt socket for the first time, my GURU had assigned me these protocols to be implemented. So I would suggest you as well to take an RFP for any of the protocols and implement that to become a Socket Programming Expert.
I have written this tutorial to keep IPv4 in mind but now we have IPv6 available. This newer version of IP protocol has different address structures and other different concepts. So you should look forward to learn IPv6 as well.
Second point is that, my tutorial teaches you very basic concepts of Unix Sockets and you still need to learn lot of socket concepts.