Spider Man 3, specifically. Spider-Man was a fantastic intro, and Spider-Man 2 was one of the best superhero movies ever made. My ideas:
1. No Sandman! (Hayden Church gave a wonderful performance, but his character was unnecessary and took time away from the completion of the Green Goblin arc, and the movie's main villain, Venom)
2. Make Peter Parker suave rather than emo! (like The Nutty Professor, specifically the original Jerry Lewis version) Peter needs to show that he's a dick, but not make an idiot out of himself. He should be the stereotypical "player", which is a complete 180 to his normal self)
3. More Venom! (He's the guy we came to see, and we shouldn't have been disappointed. This would have been the better role for Hayden Church, as he has the right build for Venom. The final showdown would have been much cooler, since both Spidey and Venom are similar to each other in power, but with specific physical differences)
4. DON'T RETCON UNCLE BEN'S DEATH! (If Uncle Ben was killed because of Sandman being spooked, rather than being shot by the first killer, then it technically isn't Peter's fault that his uncle was killed, taking away his motivation for being a hero. You wouldn't change Batman's history so that his parents die in a car crash, so why change Spiderman's back story?