Barrel position is key here. Place the barrel somewhere in relation to the bird. This gives you an advantage, so when the bird arrives, you can keep it in sight all the way through to the point where you feel comfortable to shoot it.
As the bird approaches pull your gun up to the bird, pull through the bird, firing and keeping the gun moving. Make sure that you keep your head firmly in contact with the stock, this should ensure a clean kill. Putting your barrel over the target can cause your head to lift, and/or maybe your left eye could take over if you shoot with both eyes open because the target is underneath the barrel. Both of these will make you less accurate. If your head lifts, even by one cm, out there the shot can change by anything up to 2 or 3 feet.
You need to keep your concentration. If you have a few partridges coming at you, the excitement factor kicks in. On the drive, focus on your peg and your zone.
If a covey of partridges comes over the line of guns, look through it, not at it and you will naturally pick out a bird to shoot. Once you’ve selected a bird to shoot, don’t change your mind, stay focused on that bird and taking the shot before thinking about your second bird.
As with all shooting, clay or game, footwork is one of the most important things to remember. Place your feet in the position you need to be shooting at, rather than the position at which you’re locking on to the bird.
So if you read that that the bird is going to go left to right in front of you (this is why reading the drive is so important), set your feet for the kill point. If you don’t, you’ll be off balance and it will all go wrong!
Get your feet right and the shot will be right.