Soresu, or Form III, is one of the most famous lightsaber forms due to its most famous practitioner - Obi-Wan Kenobi. Like all lightsaber forms, form 3 was developed as a reaction to changes in weaponry and fighting styles. Specifically, form III was developed after the advent of blaster weapons.
Known as the Way of The Mynock or the Resilience Form, Form III offered protection against blasters in a way Form I and II could not. Like the duelling form Makashi, Soresu was built on the conversation of energy and economy of movement to deflect and redirect attacks.
However, the form did lack many offensive options which put the form under scrutiny from some Jedi. As a result, more aggressive forms such as Juyo/Vaapad would be developed to address this. But for those who can master it, Soresu is a great style for your duelling saber sparring...
What made the Soresu form unique?
Soresu was typically practiced by Jedi of smaller statures who couldn't rely on raw power to defeat enemies. It is perhaps the most iconic of styles in terms of how it relates to the Jedi values of non-aggression - as Soresu is designed to defend rather than attack.
The traditional Soresu opening stance is to hold the blade in your rear hand, facing towards the opponent. Take a wide stance, extend your empty lead hand and hold yourself at brace ready. From here, the stance is all about anticipation and deflection - which required a great deal of calmness and presence of mind.
The main strength of Soresu comes against blaster fire. A strong Soresu user could not only deflect, but send blaster bolts back at their attackers. Some users could wade through salvos of blaster fire unharmed, creating a 'circle of protection' by meditating as they advanced and continually deflected fire using the force to anticipate the shots.
Mace Windu, inventor of Vaapad, remarked on the effectiveness of the style when he asked Obi-Wan Kenobi if it was greater to have invented a 'killing form' like Vaapad or master a classic form as Kenobi did. The implication in his words is that for a Jedi, mastery of a defensive form is more in-keeping with Jedi values.
Who practiced Soresu?
Obi-Wan Kenobi is the most famous Soresu user. He was originally trained in Form IV under Qui-Gonn Jinn, but changed styles when his master was slain to better address his own weaknesses.
While he would be bested in a duel by Count Dooku who was a master of Form II, Obi-Wan did not give up. He persisted in learning his chosen style beyond the limits of what anyone else has ever tried before. He continued to use Form III as he defeated some of the most fearsome duellists of his era, including General Grievous and Asajj Ventress.
Kenobi's greatest test came against Anakin Skywalker when his former apprentice turned to the dark side. Battling in the fires of Mustafar, Anakin used all of his rage and anger to try and strike down his former master. Despite the relentless attack, Kenobi was able to withstand, block and parry all of Skywalker's attacks.
Soresu proves most efficient against wild attacks, which is exactly why it's so useful against a fighter like Anakin. The anger and aggression exhibited by the man who would be Darth Vader was made to work against him by Kenobi's defensive skill.
Even Kenobi's famous "It's over Anakin. Don't try it!" quote stems from the fundamentals of Soresu. By understanding defensive positioning so innately, Kenobi knew having the high ground meant he had a fight-ending advantage - and was empathetic enough to warn Anakin about it. The headstrong Sith, however, famously ignores Kenobi's words and is swiftly dismembered as a result.
Soresu in Real Life
Like all of the fictional lightsaber forms, Soresu has its own origins in traditional swordfighting techniques. Many of the style's inspirations come from the way a swordfighter must adapt to face multiple attackers. Unlike the fencing-inspired style of Makashi, Soresu is more about deflecting and blocking.
As a lightsaber duellist, using Soresu means understanding that the 'attack is the best defence' analogy is not true. The best defence is...a good defence. Surprise?
To get started, you need to learn the opening Soresu stance and begin anticipating where a blow will come from. You then need to learn how to deflect and parry blows, relying on defence over offense. Let your opponent get tired with their attacks before catching them with strikes to the wrists or legs.
To wield Soresu adequately, you want a duelling saber designed for defence - this means one with a good hilt. A saber that has a crossguard such as the famous Kylo Ren Crusader design would also be a good choice so that you can avoid disarming strikes as you defend.