package foo;
sub new 
{
   my $class = shift;
   # Default initialization
   my $self = { 'some_scalar'        => "",
                'another_scalar'     => "",
                'some_array'         => [],
                'an_array_of_arrays' => [], # also
           };
   # initialize $self from @_.
   # you may be calling package functions which expect to shift in a ref to data.
   bless $self, $class;
}