The next description was taken from 2 postings from rec.kites and must be the clearest one possible...

In case anyone's not sure, the 540 Flat Spin goes like this

• The kite starts flying directly downwards towards the ground.
• At some point before the kite hits the ground (and the lower you go the more impressive it is, but also more risky), you throw both arms forwards so that the kite flattens out, with the nose pointing away from you and the front of the kite now facing the ground.
• A gentle tug (I tend to use the word "pop") on one line should start the kite rotating flat as if it was impaled on an imaginary pole sticking up from the ground.
• After 540 degrees (1 and 1/2 rotations), the kite should still be flat facing the ground (or nearly flat) but with the nose now pointing towards you.
• A gentle pull on both line makes the kite sit up and fly off upwards.

As simple as that? Well actually, no. There are a few subtle things that you have to get right to perform the 540 Flat Spin and unless you know what you're looking for, they can be difficult to get right.

Practice killing the kite out like this, holding it for a second and then recovering from this position. To do this, either walk forwards and let the kite drop the the ground, or to recover in flight, take up the slack on the lines, pulling more on one line than the other, to get a half-twist-come-turn back out of the killed position.

Not all kites like to be killed fast (some prefer a more gentle approach) so you may need to experiment until you find what works. These kites *will* do a Flat Spin, but generally they need a little more accuracy from the part of the flier. Dedicated trick kites tend to kill and spin faster with more tolerance for user error.

The reason is this: when you pop with the right hand, that wing should be slightly nearer to you than the other. When this is the case, the kite is already a little way into the rotation and will continue into the Flat Spin much easier. To get the right wing nearer, you push the left wing out further and faster. Just to confuse matters, the kite is upside down and the right wing is actually on the left as you look at it...

Waay-haaaay! It's Crap ASCII-Art time!

Looking down from above in a bird's eye view, the kite flier on the left has killed the kite evenly. The flier on the right has thrown his left arm further forward which has made the kite rotate a little in an anti-clockwise direction. The kite is now set up for the pop.

 
Nose  --->      *           *
                |            \
T/Edge -->   ___|___          \  _/
              \   /            _/ /
               \ /           _/  /        ( weird looking kite, eh? )
Lines --->      X             \ /          
(crossed)      / \             X                      
              /   \           / \                    
                              m  \                
Hands --->    m   m           |   \               
Arms  --->    |   |           \   m
Body  --->     \O/             O_/

Now give a small but firm tug with your right hand and *immediately* let lots of slack into both lines. Another step forwards at this point is often a good idea to achieve this.

Watch the kite. If the pop makes the kite "jump up" into the air instead of rotating then you either pulled too hard or the kite wasn't set up properly - perhaps you killed the kite too evenly? If the kite starts to turn but then tensions the lines and stops, then you need more slack in the lines. Try taking that step forwards.

If everything goes according to plan, the kite will rotate one and a half times and then recover. Most trick kites will usually recover themselves as they complete the final part of the rotation - the wind catches them and off they go. Try and gauge the slack in the line so that you can re-tension at exactly this point to get a clean and controlled exit from the trick. Some kites might need a little tension as the final rotation completes to help them recover.

The center of the window is most dangerous, especially in a ballistic wind. Imagine the kite screaming down towards the ground in a mad suicidal dash, only to stop at the very last minute with a loud crunch as the frame splinters, tearing through the sail and embedding the spine firmly in the ground.

The moral: practice in lighter winds, off to one side of the center of the window. If you go too far out, you can find the kite sliding sideways as it spins. This is the basis of an advanced Flat Spin trick - the Flash, but for beginners it can be a little off-putting. The left(ish) side of the window is slightly easier for right-handed poppers and vice-versa.

OK, let's try something different.

Instead of flying directly down to the ground, try flying out from the top center of the window, down towards the bottom left hand corner of the window. You should aim to reach the point where the kite slows down and almost stops by itself (ideally without hitting the ground). The nose of the kite should be pointing towards 7 or 8 o'clock on an imaginary clock.

Now execute the same 540 Flat Spin maneuver as described above *but* doing everything a bit slower because the wind should be holding the kite almost stationary - "parked" at the edge of the window. A nice gentle kill (push that left hand forward!) followed by a smooth right hand pop should be enough to start the kite spinning smoothly around. Remember that it needs slack in the lines once it's started to get all the way around.

If you prefer to "pop" your left hand, then fly out to the right side of the window, push your right hand forward and then "pop" with your left.

You'll probably notice that the kite slides back in towards the center of the window while it's spinning and it probably won't spin totally flat to the ground. In fact, the trick you've just done is a 540 Flat Spin variation that has a name of its own: The Flashback. Because it happens more slowly out at the edge of the window, it's a little easier to learn than the straight 540 Flat Spin.

When you've mastered the Flashback you can try coming in a little from the edge of the window, speeding up the dive, and heading more downwards than out. Eventually you should be doing straight 540 Flat Spins without thinking about it.

Let's say that you're going to pop the 540 with your right hand. This is how I would do it.

As you bring the kite down towards the ground, power up the kite by pulling your hands behind your back. Time this so that you are just at the end of the back stroke when the kite is ready to be thrown out. At this point your weight should be on your back foot (left foot). So there you are arms down behind your back, weight on your back foot (left foot) and the kite about 6' off the ground.

Now, all in one movement transfer your weight through your right foot and onto your left in one step, making your left your front foot. Also throw both hands forwards while doing this. This sudden movement forwards will transfer all the forwards speed that you built up by pulling back into an away from you direction. (If you make a note of how far back your hands are at the start of this and then check where they are at the end, you'll see that you've managed to move forwards by at least 6' (just like that...)

You should stunt (hold back) one hand as you throw them forwards, in this case it would be your right hand. Let it come to just in front of your waist, 6" max. As the kite hits the end of the line give a small flick of the right wrist, like cracking a whip.

Why?

Because having your left foot forwards will turn your whole body around to the right, making your left shoulder relatively further forward than your right. Try this simple test, put your left foot forwards and try to look to your left. You should need to look over your shoulder to see, now look right.

As you get the 540 down, you'll find that you need less movement to perform it. At this point you can get away with just transferring your weight from your back foot (left) to your front (right) without the step.

It's tough to perfect the technique to get a smooth spiral upwards, at first it's more of a "Spin, Jerk Up, Spin, Jerk Up, Spin" kind of motion.