Your question is not entirely clear as to which row should be the first
blank row... 11 or 12. Assuming 11, try this macro...
Sub InsertRowsEveryTenthRow()
Dim X As Long, FirstBlankRow As Long, Increment As Long, U As Range
FirstBlankRow = 11
Increment = 10
For X = FirstBlankRow To ActiveSheet.UsedRange.Rows.Count Step Increment
If U Is Nothing Then
Set U = Rows(X)
Else
Set U = Union(U, Rows(X))
End If
Next
U.Insert
End Sub