Below are the four bread and butter, essential shots that every sword and shield fighter should know how to use.
The high cross. Extend the arm at the shoulder, internally rotate the shoulder, and pronate the forearm. The sword moves through 180 degrees and hits the opponent in their right arm or possibly chest. This is the most commonly thrown shot in foam fighting. What makes it so good is that if the opponent is starting a shot or has just thrown one, this will hit because their arm is out of the protection of their shield and hand guard. When the shot lands, even if it hits the opponent's guard it blocks them off from throwing any high shots. The high cross is not very good at hitting an opponent who is not swinging, however.
The shield side shoulder. Similar to the high cross, extend the arm at the shoulder, internally rotate the shoulder, extend the arm, and pronate the forearm such that the sword strikes with the false edge (the part that usually faces you) over the top of the opponent's shield. This is called a "wrap" because the sword rotates at the hand in order to wrap around the shield. This is a kill shot if thrown properly, which means that if your opponent goes for a high cross or even chops your arm off mid-swing, you still win the fight. The closer you are to your opponent the harder it is for them to block. This shot takes less time to throw than the high cross or sword side hip, and so returning quickly to guard is important so your arm doesn't get sniped. It also works better if you are taller than your opponent, but that's not an absolute requirement. Disadvantages are that if your opponent sees you start this shot they can throw a super fast chop to your arm and take it. This is also the shot that wrecks people's shoulders in the long run since mechanically it's essentially a baseball windup.
The shield side hip. Starting with the forearm supinated, extend the arm at the shoulder and elbow such that the hand moves downward toward the edge of the opponent's shield. Then pronate the forearm and continue extending such that the sword wraps around the opponent's shield to hit them in the hip or back. This shot is a kill shot that's harder to counter than shield side shoulder since you're better covered by your own shield when you throw it, but it has some serious flaws. Many shields tend to have excellent coverage in this area and you may not be able to land it even at ultra close range. Some fighters may also have their elbow in the way somewhere and what you think is a kill shot turns into just the shield arm. Finally, you may end up throwing too low and hitting your opponent in the leg, which is no good. (Leg shots are my least favorite shots because they do relatively little to help you win the fight, and if you throw a leg your opponent has some time to try and hit a better shot on you.) In addition, everyone's definition of "hip" is a bit different and unfortunately this is an area where people tend to cheat.
The sword side hip. Adduct and internally rotate the shoulder and flex the elbow slightly to bring your hand over to your opponent's right side. Then with the forearm pronated, supinate the forearm and extend at the elbow, allowing the sword to turn over and strike the opponent's torso or hip with the false edge. This is a powerful tool in your arsenal, but by far the hardest to learn. Normally the opponent's sword blocks this shot, but if they are throwing a shot, especially the high cross, or anticipating having to block high, their sword can no longer defend, and the shield does not always move back across the body to cover. It can also be difficult to read that this shot is coming. It is usually a kill shot but sometimes you can take the right arm instead. The worst case scenario is going too low and getting a leg. The Achilles of sword side hip is that it's relatively easily countered with a high cross, which is the most commonly thrown shot, so you will sometimes get unlucky and lose your arm. You can try and make up for this by pulling your shield up and over to cover your arm while you throw, if your shield is an accommodating shape.
Here is a great video series showing the body mechanics for each of these shots (they use slightly different nomenclature): https://www.youtube.com/watch?v=1qbnCLcjDcg&list=PLjyWZ805aKm823MBhtVw0yykb9-Y62I01
I hope this helps you improve your fighting game!
Sir Rat of Gestiguiste