There are several types of saves a goalkeeper can perform, but knowing when to use which is entirely situational. You have your basic standing saves, kneeling saves, medium and high saves, forward vaults, tweener saves and diving saves. Let's see when and how you should use each:
Standing Saves – This is not a recommended save when the ball comes rolling at a high speed, especially if you're playing on a wet pitch. Basically, what you'll be doing will be bending down forward from the waist, collecting the rolling ball and bringing it up to your chest. Simply allow the ball to roll up on your wrists, with your legs straight and back arched and your feet close together (so that if the ball accidentally rolls past your hands, it doesn't go through your legs). Then clutch the ball against your chest, protecting it and straighten up your back.
Kneeling Saves – The kneeling save is slightly similar to the standing save in what regards a goalkeeper's arm work, however besides bending forward from your waist, you will have to take a knee and keep the other one almost perpendicular to the one on the ground. This position of the legs reduces all chances that the ball might slip between your legs and into the goal. The kneeling save can be performed against balls that come at you at higher speeds in comparison to the standing save.
Medium and High Saves – If the ball is coming towards your chest or head area, keep your shoulders square on the oncoming ball and bend your arms forward, keeping them slightly tensed. Use the elbow flexion to dampen the ball's incoming force rather than your shoulders. Your shoulders will be used as a last resort if the ball is too powerful to handle. The reason you shouldn't take your shoulders back and dampen the ball's force using them is that you might not be able to fully stop the ball and it might hit your chest, bouncing off.
Now, unlike other types of saves, medium and high saves will require a bit more practice in the mechanics and less on positioning. When you get to a point where you can catch the ball and safely bring it to your chest in a full stop, you've mastered this type of save. One last thing, on powerful shots from close range, it will be extremely difficult to secure the ball, even if you use your fingers, elbows and shoulders as a force dampener. It might be better to punch the ball upwards or sideways in this case, or you might risk giving the other team a rebound opportunity.
Forward Vaults – The forward vault is an extension of the kneeling save. Use the same mechanics as in the kneeling save, but instead of standing up directly with the ball secured to your chest, vault forward to the ground and extend your arms beneath yourself with the palms upwards, trapping the ball between your fingers, wrists and forearms. Then, after the ball's force is dampened, pull your arms back and trap the ball between your arms and chest. Best used on slippery pitches, where stopping the ball is trickier and securing it tightly becomes even more important.
Tweener Saves – A ball that comes rolling to a goalkeeper's side is usually referred to as a tweener, hence the name of this type of save. Basically, the mechanics for this save are similiar to forward vault's, but since the ball is coming at your side, you have to vault sideways. The only difference between the two is the leg work. With the tweener save, you will have to extend your lead foot in the direction of the save, bending the trailing leg enough to close the space between legs. The trailing leg bends to close the space. At younger ages we teach the player to to do the same sequence of movements with the knee touching the ground but, For older more advanced keepers the knee does not touch the ground.
Diving Saves – The diving save is probably the most spectacular a goalkeeper can perform. When a ball is far enough from your current position that a tweener save isn't enough, you will have to perform a diving save.
This involves pushing yourself hard into the ground with both legs, fully extending yourself sideways in the direction the ball is aimed at and releasing the jump. Luckily, you'll be able to deflect the ball off its course towards the goal. Remember that a ball can rarely be "saved" and secured from a dive and even if you do grab hold of it, the fall has a chance of shattering the ball away from your hands. So, depending on the situation, it might be best to deflect it rather than try to save it.