1. If you have an ethernet cord direct connected to your MODEM, you do not need to port forward. If it's connected to your ROUTER, than you do need to port forward.

2. Make sure your friend is typing the server address in the following format:

EXTERNAL_IP_ADDRESS:PORT

For Example: 70.44.136.118:25565 (This is your EXTERNAL IP Address. You can find it by simply typing "My Ip Address" into internet search.)

WRONG: 192.168.1.35:25565 OR 10.0.1.35:25565 (These are LOCAL IP Addresses, and are used to connect to LAN servers on the same internet connection as you.)

3. I personally reccomend "Port Map" if you're doing this on a Mac. If not, I reccomend "Simple Port Forwarding"

4. Make sure you can connect to the server using the EXTERNAL IP Address instead of Localhost.

5. Make sure you have enough RAM Allocated to the server "At least 1 GB Minimum" or it will crash when more than one person logs on.

6. Copy and paste what the server console says when your friend tries to log on here. If it says something like:
"[SEVERE] Reached end of stream for /70.44.136.118"
than your internet connection is simply not reaching your friend due to a firewall, proxy, or lack of speed. Make both a UCP And TCP exception to your firewall for the server port (25565 Usually), so that you can keep the firewall running. Turn off any proxies you have. Make sure you have a reasonable internet speed, somewhere higher than 25 Mbps is preferable, and a 100 Mbps or even 1 Gbps ethernet Connection is ideal, as its fast, and you get to avoid the whole port forwarding process. Under 15 Mbps is too slow and will NOT work.

7. Since some of you are using Phone Tower Internet (A Verizon/AT&T/Verizon Hockeypuck, Jetpack, or USB Internet Stick), you'll run into a much more complicated issue with port forwarding: You are not the connection's host. Your External IP address is subject to change at any time, and you have no access to a Router or Modem. Contact the Company of the Internet for information on how to port foward.