This is an odd thought experiment. If you were in charge of the Spider-Man books, and wanted to get sales on Amazing Spider-Man as low as possible, what would you do?
Amazing Spider-Man is currently Marvel's best-selling non-Star Wars title, so continuing what they're doing now isn't the way to sink the book.
Here are some of my thoughts on how to destroy the Peter Parker Spider-Man...
1. Fire Dan Slott. Make it as messy as possible so that many of the people who like his work drop the book.
2. Start overexposing the character. Launch new monthlies, or make Amazing Spider-Man a weekly title to make it more expensive to follow Peter's adventures.
3. Hire writers who aren't very good and very punctual. If their pitch includes heavy focus on the supporting cast, or on a new character to give audience perspective, let them do that kind of stuff.
4. Insist on a lot of references and flashbacks to obscure periods in the character's history.
5. Make Sarah and Gabriel Stacy supporting characters.
6. Pick artists who aren't very good and very punctual. Don't be afraid to have multiple artists contributing to a single storyline, if not a single issue.