Although each book is intended to be a dystopian novel, they both exhibit stark contrasts from each other.
Orwell's 1984 uses a society at large with a focus on just a few characters. This society contains a hierarchy based on power and influence. Those in power pride themselves on the ability to control the entire rest of the society. In Golding's Lord of the Flies, we do not see a society at large, but a microcosm of a society, and of only children at that. His purpose for showing just a piece, and a young piece devoid of adult influence served to demonstrate what would arise from a people removed from the influence of their government. A new "government" would emerge, and it did not look that much different than the old one that he is likely commenting on from his current era.
Character development differs significantly. The Winston Smith character of 1984 stands for the everyman. He wants to challenge the government because he is intelligent enough to determine that something is wrong, but he is so entirely average that he really doesn't have the power to do so. The closest we get to an everyman in Lord of the Flies is Ralph, yet he is made leader for a large portion of the book. Both Ralph and Winston go through great tragic mental anguish in order to come to a new and defeated understanding of the new world, thus there is indeed similarity. The group of boys certainly develops a hierarchy as the society in 1984 did, but they do so without realizing it.
War and useless killings that go completely ignored happen in both books which demonstrates that both authors had a similar perspective about the post-WWII environment they wrote their novels in.
Both books address a perception of human nature and the way that human nature will respond to a vacuum of power or a lack of restraint.
In 1984, Orwell shows that absolute power corrupts absolutely and that no one appears to survive with their ideals intact. In Lord of the Flies, Golding demonstrates that the evil inside of everyone is real and that it is down to individuals to decide whether they will control it or not.
Both books are written from a third person perspective and both of them are responding to political and philosophical ideas of the time.