{!! Form::select('month', [null => 'Month'] + $months, null, ['class' => 'valid', 'required']) !!}
//$month is an array passed from the controller ['January' => 1, 'etc']
Then use validation to ensure that a month has been selected. As @pmall has mentioned you cannot pass a disabled attribute from within the array to the view. If you really needed this you'll have to create it manually using a loop that has a check to see if it is the first option and if so to add the disabled attribute to it.