Make sure your client pack is working well. No unresolved item ID conflicts (check your FML client log).
Create a folder for your server. We'll refer to that as SERVER.
Install Forge server into that folder. http://files.minecraftforge. http://files.minecraftforge.net/
Copy the config and mods folders (and any other pack specific top level folders like Flan or Chocolate) to SERVER.
Remove any client only mods from SERVERmods. This would be things like DamageIndicators, ArmorStatusHUD, BloodParticles, Optifine, etc.
Start server with a command like: java -Xmx2G -Xms2G -XX:MaxPermSize=128m -jar forge.jar nogui
That's it.
