1. You have to create a user: prosody
2. And a group: prosody
3. You have to create these 3 directories:
   mkdir -p -m750 /var/lib/prosody
   mkdir -p -m750 /var/run/prosody
   mkdir -p -m750 /var/log/prosody
4. Owner and group of both dirs have to be set to the previously created
   ones:
   chown prosody:prosody /var/lib/prosody
   chown prosody:prosody /var/run/prosody
   chown prosody:prosody /var/log/prosody
5. Configure prosody config file: /etc/prosody/prosody.cfg.lua
   There is already an example file included in /etc/prosody/

NOTE: Step 1-4 can easily be done by 'sh config-helper.sh' in current
directory.

Have fun :-)