First, the best push kick in the world belongs to Ken Alwell. His command of the shot is phenomenal. He's won championships both on Tornado, and Tournament Soccer.
Ok, let's start with the mechanical keys to the shot:
First, the best p.k.'s are not necessarily a brute force shot. The most successful one's are the players that have the full command of the whole shot, with all the options. What makes the shot so successfull, is the fact that you have at least seven options off the set at any one time. Properly executed, the goalie has little chance of shutting one down. My personal keys to shooting the p.k.: I have a balanced stance, I don't stand to far back from or behind the rod, the secret is to make it hands and wrist, not shoulder and arm. I have a fairly loose grip on the handle, loose muscles are faster than tight one's. It gives you much more snap to the shot, and makes hitting the ball square much easier. I personally put my thumb and forefinger over the handle, but this is a personal thing, whatever helps you hit the ball the hardest.
I start the ball on the outside box line. I feel it gives me the best starting point, and makes the straight angles easier to hit. Even though it looks like the ball travels a long way across the hole, it's actually a short stroke. It's really less than a 3/4 pull shot, as far as rod movement goes.
I position the ball directly under the rod when using new 'fuzzy' balls, or balls that are fairly sticky. With really slick balls I might move the ball just a little bit behind the rod, but not much. This helps you to 'hit' the ball, rather than 'throw' the ball into the hole. You require much less back swing, and it's easier to go straight through the ball into the hole.
Ok, those are basic setup tips, let's start firing the ball in the hole. When I'm warming up, or just working on my timing, I'll shoot a rack or so of balls just in the middle of the hole, not thinking speed, just the move through the ball into the goal. My key on hitting the long shot, I play 'bowling' with the center man. I concentrate on where I want to hit the ball, usually the #6 dot, then I watch the center man go to that dot, then down through the ball. If you can imagine ball set up like a push shot, and you want to make the same motion forward and through to the hole, that's the push kick stroke. Don't concern yourself with speed to begin with, just consistency with the stroke. Speed will come as your confidence raises.
The 'inside' shot. The dinks, angles, first hole kicks are what will make the p.k. work. I have seen maybe two or three p.k.'s in my whole life that were virtually unraceable, but they were so long crazy, they weren't that hard to block. The truly deadly shot will involve the entire hole.
I use two different first hole dinks, the standard semi-off speed dink that will move a guy racing you out of the first hole just enough to slip it past him. I also shoot a 'power dink' a lot, it's basically a hard fast push shot to the first hole. This will work best when the goalie thinks they have your movement down on the slow dink.
Probably the most effective dink is the middle slide. I use this a lot and score probably more with it than any other shot in the bag. This dink I start very fast, same speed as my long, and just 'nudge' the ball forward, so it slides across the hole to the far corner. It's a devastating shot, and will break a defense down very quickly.
Next, and just as valuable are the far and near straight angles. This is just like a straight in with a pull shot. I just hit the far or near corner. This is most effective when the goalie is trying to bait you, and they can't see those two holes. If I see the goalie trying to bait me, I'll just sit on them, and fire the straight angles when they open them up. Again, it will really tighten up a defense, and make them hesitate and make mistakes trying to defend you.
Lastly, is the first hole smash. This was probably the hardest shot to learn, but again, it's very valuable. This is putting it in the first hole as fast and hard as your long kick. It's a little tricky, because you must come back for the ball. I push it out, then bring the three rod back to the bumper and hit it straight into the first hole. That shot will completely throw off a racing goalie. After a few first hole smashes, he'll be hesitating on every move you make, and you can just feel free to launch longs on them the rest of the match.
I really enjoy shooting the shot, I feel it's almost an art form when it's done correctly. I also feel when it's done correctly, there isn't a harder shot to block.
I hope this helps Jack.