IT is perhaps the biggest mystery of flying since the Wright Brothers finally cracked it all those years ago. Just how do you get to those big fancy seats at the front of the aeroplane, where the wine is vintage, the steak done just the way you like it, and the smile of the cabin staff just that little bit broader as they lay out your linen tablecloth and proper plates? It is the mystery of the upgrade, that moment when a cheery person in crisp uniform and bearing clipboard approaches you in the seemingly interminable queue for check-in and utters the magic words: ''Excuse me, Mr Jones, we would like you to offer you an upgrade to business class today. Would that be OK with you?'' In nine point something cases out of 10 it will be more than OK with Mr Jones as he feigns surprise and follows the clipboard to the nearby, but naturally much shorter, check-in area for premium cabins.

He has crossed the great divide between the seething masses of economy travel, where the price of a ticket for travelling 3000 miles across the Atlantic can work out about 10p a mile, to the high-comfort world of the premium traveller.

Up at the ''front of the bus'' as it is affectionately known in aviation circles, he will find seats bigger than the armchairs in his living room and enough space to stage a mile-high game of headers.

If we take the example of American Airlines, which has a seasonal operation between Glasgow and Chicago and is the preferred choice of many travellers seeking to avoid the hassle of changing terminals at Heathrow, then the trip to the ''front of the bus'' is a treat.

There are 30 seats in business class and eight in first, and as well as the food and drink being of the highest calibre, the juvenile pleasures of a wee bag of goodies like daft socks, toothpaste, and facial spray which makes you feel you have been treated with formaldehyde are all there. The passengers are treated to a level of service which for someone weaned on Dan Air charters to Malaga is a whole different world. Efficiency, poise, and charm seem to be the key elements of being clippie on this part of the flying bus.

But back to the upgrade thing. In saying that Mr Jones ''feigns surprise'' it is perhaps being unfair but let no-one lose sight that in many cases there are people in the queue around you who are expecting just such an approach.

They are the fortunate few who have been targeted by the sales department of, let us say, Flyaway Airlines, as being a good candidate to be moved from economy to a premium seat.

There could be any number of reasons but the main one, in the words of one experienced airline sales person, ''is to make sure the punter comes back the next time''. The flight has to take on board sufficient food and drink for all seats, it is not just like nipping down to Safeway when you know how many folk are coming for their tea.

So if Mr Jones is left down the back and the seat on which his bum was potentially to be remains empty, the grub is wasted and the wine remains on chill.

But what to do if you or your firm are not on the target list of the clever sales people at Flyaway HQ who have noticed that full-fare economy tickets are being purchased and do not really mind giving away the little extra for business class? There are three simple rules. Look the part, be patient, and keep your nose clean.

The first is just as simple as it sounds, smart appearance is far more likely to attract the ground crew member with the clipboard than jeans, a T-shirt and sannies.

There is no need to get togged up like some demented member of the Jack McLean fan club but denim and poly bags are definitely out and the look of a seasoned traveller complete with designer creases and well-worn but clearly expensive luggage is in.

The patience part comes because you never know until the last minute what is going to happen and it could be just as you hand over your ticket that the magic code ''upgrade'' appears on the screen. The fortunate few, you see, who actually buy premium tickets have the luxury of not turning up and still getting their money back.

The last part is the most important and is two-fold. Not only is it the right thing to behave in the check-in area but when you get on the plane showing the best of order is vital or, in the words of another industry person, ''you'll nae get asked back . . .''

It never fails to amaze those airline people that no matter how much alcohol you lay on there is someone who wants more. A group of young but inexperienced travel agents recently lost the place in a premium cabin as the Chablis Premier Cru kicked in on top of the nine pints of heavy consumed before boarding.

This correspondent is the last person to advocate a trip on an aircraft without any ''swally'' but care must be taken at all times for two reasons. The person next to you may have cashed their life savings for this experience and the man from Flyaway will ensure that your return trip includes a stopover in Port Stanley.

Happy flying, then, and for the person with the clipboard I'll be the one with the wilted rose and a rolled up copy of The Herald.