I freely admit that I copied and pasted from a previous thread where I did actually type it all out. I copied this too:
The cloverleaf pattern is basically a square with a circle in each corner, but instead of going along the wall to get to the next circle the horse is going through the middle of the square. I adapted it from a book of arena exercises where you ride large and every time you reach the middle of a side you turn and ride to the middle of the opposite side, turning the same way you did when you left the track (so all lefts or all rights). When longeing the human is walking a square, stopping in each corner as the horse does the circle.
Start at the walk. You stand on the quarter line and longe your horse in a 10m circle to the left in the corner between. K. and. A. As the horse comes off the wall and onto the centre line you push the horse out so they leave the circle and stay on the centre line walking towards X and you walk parallel along the quarter line for 10m. You stop and the horse follows the contact on the line to walk a circle around you (technically it’s 3/4 of a circle). As the horse comes off the wall and reaches the quarter line you push them out and you both walk parallel to the short side across to the other quarter line, where you stop and the horse goes on the circle. As the horse comes to the centre line (now heading towards A) you walk 10m along the quarter line as you push the horse out to walk the centre line. You stop, the horse circles and you both walk across to the other quarter line back to the 10m circle in the corner between A and K.
Once you see how the pattern works you can change the circle size easily, and you can go further along the long axis of the arena between circles if you want (a good way of easing closer to the scary spot).