The best way is to use Mailmerge to labels with an Excel data source.

Or to do it using a macro, on the first ticket on your page, where you want
the numbers to appear, insert the following field

{ DOCVARIABLE varSerialNumber \# "000" }

On the second ticket insert the following field

{ = { DOCVARIABLE varSerialNumber } + 1 \# "000" }

and on the third ticket insert

{ = { DOCVARIABLE varSerialNumber } + 2 \# "000" }

You must use Ctrl+F9 to insert each pair of field delimiters { }.  Use
Alt+F9 to toggle of the display of field codes.

Then run a macro containing the following code when that document is active.
It will ask you for the number of tickets that you want to print and then
proceed to print them.  If later you want to print some more, just open the
document and run the macro again.  It will start numbering tickets from
where the first batch finished.

Dim Message As String, Title As String, Default As String
Dim SerialNumber As Long, NumCopies As Long

' Set prompt.
Message = "Enter the number of copies that you want to print"
' Set title.
Title = "Print"
' Set default.
Default = "1"

' Display message, title, and default value.
NumCopies = Val(InputBox(Message, Title, Default))
SerialNumber = Val(System.PrivateProfileString("C:\Settings.Txt", _
"MacroSettings", "SerialNumber"))

If SerialNumber = "0" Then
   SerialNumber = 1
End If

ActiveDocument.Variables("varSerialNumber").Value = SerialNumber
Counter = 0

While Counter < NumCopies
   With ActiveDocument
       .Fields.Update
       .PrintOut
       .Variables("varSerialNumber").Value =
.Variables("varSerialNumber").Value + 3
   End With
   Counter = Counter + 3
Wend

'Save the next number back to the Settings.txt file ready for the next use.
System.PrivateProfileString("C:\Settings.txt", "MacroSettings", _
       "SerialNumber") = ActiveDocument.Variables("varSerialNumber").Value

See http://www.gmayor.com/Numbered_labels.htm