I find that the best approach is to tell them. On boarding the plane, I say in a very loud voice "DO YOU KNOW WHO I AM?!". I wave my boarding pass at them and they are always impressed. (Or at least I think so... they typically frown which I think means they are worried about having someone of my status on the flight and not sure whether to address me as Sir, Mr Russ or just Russ.)
Just to be sure, I put NGCI bag-tags on my hand luggage and make sure I put it in the overhead bins with the tag hanging out so the crew can see. I also make a point of introducing myself to other passengers and telling them that if a crew member takes me to first class, it is not because I have complained about sitting next to passengers of lower status.
If I do not receive a greeting, express card or special headphones, I assume that the relevant staff-member is on work experience and press my call button and politely demand to speak to the captain. I explain my status to the captain who is suitably impressed as above.
All in all this works very well and I am always given wonderful service by QF. My only niggle is that almost every flight, a crew member accidentally spills red wine all over me. I wonder what the odds are of that? Anyway, they are always super-polite after spilling it all over me, giving me a big smile and saying that they are "soooooooo sorry!"