Free upgrades are the holy grail of air travel.

They're said to exist, although they often seem like an urban legend. And there's nothing we won't do in the hope of scoring one, even though our efforts often seem ridiculous and infuriatingly futile.

But there are ways to achieve the much-coveted free upgrade, Robin Chiang, the head of KAYAK Australia, told news.com.au. And it could be as easy as being strategic about where you book your economy seat.

To begin with, the most sure-fire way to score a free upgrade remained joining an airline frequent flyer program, Mr Chiang said.

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"And stick to one airline - in these circumstances, loyalty always goes a long way," he said.

"Secondly, passengers who have booked flex-fares or other higher-priced tickets with a class will more likely be upgraded. If you don't mind paying a little more upfront it could reap rewards at the departure gate."

But there are other ways to get perks on your next flight that are worth trying. Here are Mr Chiang's other top tips:

1. DON'T BE SHY - JUST ASK

"When you are checking in, flash your best smile and ask nicely for an upgrade. It can't hurt, right?" he said.

"The agents at the check-in desk do have some discretion to provide upgrades, but they have also heard 1001 tales of why an upgrade is deserved. So dress well, flash those pearly whites and just be your charming self."

2. ARRIVE EARLY

This one is simple - the early passenger is the one who gets the upgrade.

"I once heard of someone getting a free upgrade simply because he was the first person to arrive at check-in," Mr Chiang said.

"Sure, the chances are slim but it might just be you that lands the jackpot."

3. BOOK THE ROW BEHIND THE EXIT ROW

Sitting in the exit row isn't quite the same as being bumped up to business class - but that extra leg room is glorious, if you're willing to pay extra for it.

But there's a way you could get it for free.

"Flight attendants require exit row passengers to be physically and mentally capable of opening the exit door and remaining calm under pressure," Mr Chiang said.

The seats behind the exit row could be your ticket to free extra leg room. Photo / Getty Images
The seats behind the exit row could be your ticket to free extra leg room. Photo / Getty Images

"If the exit row passenger doesn't fit the bill, they'll look for someone else to fill the seat." And the thinking here is, by sitting immediately behind the exit row, you'll be right in the flight attendant's line of sight as they scan the cabin for someone else to take that spot.

"All that extra leg room is almost as good as an upgrade," Mr Chiang said.

4. LOYALTY GOES A LONG WAY

Put simply, the more you fly with a certain airline, the more likely you will be hand-picked for an upgrade, and rewarded. "If you can fly your way to gold status, that elusive upgrade will often become a reality," Mr Chiang said.

5. MAKE THE MOST OF YOUR MILEAGE

Buying an upgrade is widely considered the best way to spend your air miles, and Mr Chiang agrees.

"This is frequently much better bang for your buck than redeeming a business class ticket outright, particularly on long-haul flights, like Sydney to London," he said.

"Just remember to read the fine print when you are booking your ticket - some cheaper class fares do not allow for points upgrades."

6. BEFRIEND PEOPLE IN HIGH PLACES

"As in life, it's not what you know, it's who you know," Mr Chiang said.

"Mates rates also apply to flight upgrades. Know a flight attendant? You beauty. The pilot? Even better. If not, maybe it's time to broaden your horizons and make friends with people who do and go on holiday with them.

"The pyjamas in first class are totally worth it."