Don't use the same method for coming up with ideas over and over and over again. Even a good rut is still a rut.In the habit of approaching problems visually? Try writing headlines instead. Even if the idea doesn't require them.
Like to work directly with your partner? Try spending an hour or two on your own before coming back together to share ideas.
Do you normally write your ideas on a laptop or a notebook? Try using a stack of index cards and a Sharpie.
There are a bunch of ways you can approach a problem. And you should use all of them. Even if it means sitting in a different chair than you're used to.
When you find a method that works really well, you should use it as a tool, not a crutch. Don't let yourself think, "This is the way to come up with ads," because it won't be.