The novelization of Rian Johnson's The Last Jedi is already delivering on its promise of being the "extended edition." Though the book isn't out officially until March 6th, some lucky Star Wars fans have gotten their hands on advanced copies and have started sharing some of the more interesting pieces of information. And some of the most interesting facts in the book are about Supreme Leader Snoke's past and his mysterious rise to power with the First Order. There are spoilers for The Last Jedi novel ahead, so read ahead at your own risk.
According to The Last Jedi novelization, which was written by Jason Fry with the assistance of Rian Johnson, Snoke was the unexpected leader of the First Order. The last of the Imperial leadership, Gallius Rax, Sloane, the political lunatic Ormes Apolin or even Brendol Hux, who survived the Battle of Jakku did not see Snoke's rise to power and were surprised when it occurred. Snoke either killed them or had them arranged to be killed except for Hux, who he used as a tool and his rise within the First Order was not by plan, but was instead more opportunistic.
Emperor Palpatine's contingency, Operation Cinder, was engineered to destroy the Empire after his death and bring a rebirth of it, which was intended to be stronger than it ever was before. Snoke knew this and used it to his advantage, with Darth Sidious unaware that Snoke would be the one to take on the First Order, even though the Force made him aware of Snoke before his death. However, Darth Sidious could not sense what Snoke was ultimately up to before it was too late.
After the Battle of Jakku and the destruction of the Empire, the First Order began stockpiling weapons and started laboratories in the Unknown Regions as well as shipyards and storehouses. It isn't clear when Snoke stepped up and took control or if it was right from the start, but The Last Jedi novel states that Snoke saved the First Order from many enemies. It is also said that Snoke finds many Force truths in the Unknown Regions that were reportedly "waiting to be found." The book goes on to say that Snoke and Luke Skywalker had met once before, but it is not clear if Luke knew of Snoke's evil intentions. Luke's intentions were to learn more about Jedi lore and Snoke reportedly respected that he was out looking for truth.
It appears that Snoke was also looking for his truth in the Force and might not have always have been evil. When Snoke was younger, he learned that the "future is always in motion" and said, "Be careful or die." Snoke now realizes that the Force visions are "often incomplete." Additionally, it is revealed that Snoke originally wanted Rey as an apprentice and did not want her for his power like Emperor Palpatine needed Luke Skywalker. It's also shown that Snoke contemplated killing Kylo Ren, even though he believes that Ben Solo is capable of greatness. All in all, that's a lot more about Snoke than we knew previously and should go a long way in helping out fans who were disappointed in the lack of Snoke backstory in The Last Jedi. You can read more about Snoke over at Dork Side of the Force.