[Intro] An appropriate intro would be to simply strum or pluck G for a few measures.
It shouldn't go on for to long, and, honestly, I don't think you really need one. 
Simplicity is best with this song!

             
Silent night, 


holy night,
            
All is calm, a


ll is bright
             
Round yon virg

   
in Mother and 

Child
             
Holy Infant so

 
 tender and mi

ld
            
Sleep in heave

      
nly peace,
           
Sleep in heave

    
nly peace.

             
Silent night, 


holy night,
            
Shepherds quak

  
e at the sight

,
             
Glories stream

      
 from heaven a

far,
             
Heavenly hosts

      
 sing halleluj

a.
            
Christ the sav

         
ior is born,
           
Christ the sav

       
ior is born.

             
Silent night, 


holy night,
          
Son of God, lo

ve's pure ligh

t,
             
Radiant beams 

     
from thy holy 

face,
             
With the dawn 

   
of redeeming g

race,
            
Jesus, lord at

        
 Thy birth,
           
Jesus, lord at

           
 Thy birth.


----------------------------------
These chords can be applied pretty well to any of the other verses. 
I hope you enjoy it. Merry Christmas and Happy Holidays!