Originally Posted by Misco60

That's exactly how I do it: I find a good fare using just the origin and destination, and then gradually add the routing points.

You don't need the X in the routing codes: you can just enter "LHR JFK LAX". You have more chance of finding a valid routing by using multiple routing points, e.g. "LHR JFK,PHL,BOS LAX" which means route via LHR and (JFK or PHL or BOS) and LAX.

Unless you are bound to specific dates, I'd use the Calendar view rather than specifying dates. This tends to return more results.

And don't be in a hurry to book anything unless you're very happy with the fare. In my experience, the best deals appear 3-6 months ahead of travel, and this is about the timeframe within which I book my own flights.