LongListSelector: Item tap?

You could null your LongListSelector’s SelectedItem at the end of each SelectionChanged event. I.e.

<phone:LongListSelector x:Name="LLS" SelectionChanged="LLS_SelectionChanged">

And the event handler:

private void LLS_SelectionChanged(object sender, SelectionChangedEventArgs e) {

  // If selected item is null, do nothing
  if (LLS.SelectedItem == null)
    return;

  // Navigate to the next page
  NavigationService.Navigate(new Uri("/nextpage.xaml", UriKind.Relative));

  // Reset selected item to null
  LLS.SelectedItem = null;
}

You’ll fire the SelectionChanged event twice, but nothing’s going to happen the second time round and you should get the behaviour that you’re looking for – (i.e Setting SelectedItem to null will trigger a new SelectionChanged event, but this second event gets caught in the if-statement)

As for the second part of your question, you might be better posting a new question.