TL;DR: Visit http://portforward.com/english/routers/port_forwarding/, find your router in the database it will explain the steps to forward ports. The only port that you need to forward to your computer’s IP where your Peercoin client is running is 9901.
Quick guide:
So, you want to help securing the Peercoin network and become a Full Active Node? But you are stuck with less than 8 connections with your Peercoin client at home :(. Don’t cry, this guide will help you to become a Full Active Node!
First you need a running PPC client:
[ul][li]Peerunity - Windows, MacOS, Linux[/li]
[li]Peercoin-QT - Windows, MacOS, Linux[/li]
[li]Peerbox - Raspberry Pi[/li][/ul]
Three things you need to know then:
[ol][li]The computer’s local IP address that is running your Peercoin’s client[/li]
[li]Your home router’s IP address or URL to access the router’s administration interface[/li]
[li]Your router’s admin credentials to change its configuration[/li][/ol]
Access your router’s configuration page from your web browser (i.e. http://192.168.0.1 where 192.168.0.1 is your router’s IP). Enter the router’s admin credentials, and navigate through the administration settings until you find a page that lets you forward ports on your local network.
You need to add a new entry on the port forwarding page of your home router’s administration containing:
[ul][li]
Your computer’s IP address (the one running the Peercoin client)[/li]
[li]The port number 9901[/li]
[li][OPTIONAL] If the protocol type is required choose TCP only or both (TCP+UDP)[/li][/ul]
Save the settings, and restart the router if needed.
You can test if your port number 9901 is open (your Peercoin client must be running) by visiting the following page: http://www.yougetsignal.com/tools/open-ports/
If the port 9901 is open, then congratulation, you are now a Peercoin FULL ACTIVE NODE!!! 
You will then notice an increase of network connections on your Peercoin client (more than 8 connections)
Note: Only one of your Peercoin clients at home can become a Full Active Node. Forwarding the 9901 port will only allow one single local machine’s IP.
Here are the same steps in detail:
1 - Finding your local IP address is easy, you can visit the following link:
For Windows, MacOS, Linux:
https://en.wikibooks.org/wiki/Finding_Your_IP_Address#Finding_Your_Local_IP_Address_.28broadband.29_or_Global_IP_Address_.28dialup.29
For Windows, MacOS (illustrated):
http://kb.linksys.com/Linksys/GetArticle.aspx?docid=d02ed3aa3e704caea42f5c007b8c6472_3996.xml
Your local ip address should look like: 192.168.xxx.xxx
2 - Finding your router’s IP address is also easy
For Windows, MacOS (illustrated):
http://kb.linksys.com/Linksys/GetArticle.aspx?docid=d02ed3aa3e704caea42f5c007b8c6472_3996.xml (Router’s IP = Default Gateway)
On Linux or MacOS type the following command:
netstat -nrWhich will return a bunch of lines, the one we are interested in starts with “default or 0.0.0.0” and looking like:
0.0.0.0 192.168.0.1 0.0.0.0 UG 0 0 0 eth0192.168.0.1 is the router’s IP address for your eth0 interface.
You should now be able to access your router’s administration interface via your Web Browser at this address:
http://YOUR_ROUTER_IP_ADDRESS/, for example: http://192.168.0.1/
3 - To access your router’s configuration you often need administration credentials (i.e. admin/admin or admin/password), those should either be written on the router itself or in the router’s guide if you haven’t changed them.
If you cannot find those credentials, there is a website that will find them for you and explain the full process to access the router administration’s page:
http://portforward.com/english/routers/port_forwarding/
You can also use google and look for: “port forwarding router +NAME_OF_YOUR_ROUTER_or_YOUR_ISP_PROVIDER” (ISP = Internet Service Provider, i.e. Orange, EE, BSNL, AT&T, etc.)
Original post: http://www.reddit.com/r/peercoin/comments/2nh911/guide_how_to_become_a_peercoin_full_active_node/