I will give it a try but rusty. Im guessing your interest is on the LAN side. or is it the WAN? Basically the same problems you will find out. Im rusty but know others will reply.
As a beginner in the past it was suggested i do the following.
Shut down the software firewall. (maybe XP and had another at the time). Only works one way, inbound.
the router is the 1st place to start. In the past with a ftp server and client has been port 20 and 21 needs to be open. Check the server software. Default is likely 20 and 21. Ports can be changed. get it working first then play. You can also set limits to how many can access like 10 at a time.
These ports have to be open in the router. Once its working you could use the server from the wan side. Using something like
http://www.dyndns.com/
Use a good software firewall for inbound and outbound. these ports have to be open too. do one at a time. (router or then software firewall). if ya have the software firewall ya won't need like xp firewall. turn it off.
If ya use dyndns then don't ping the free ver. they will shut you down. If ya have a static ip ya won't need it i don't think.
On the other hand if for a business you might be interested in more protection like VPN or other encryption.
I used the same description for remote software. Didn't get back into yet but will. they are guidelines and others know more and up to date. i would like to think it has not changed much though.
cheers.