Effective tools for brainstorming are structured methods like brainwriting, De Bono's Six Thinking Hats and SCAMPER. With brainwriting, everyone writes ideas down without speaking. Digitally, Miro and Mural work well as visual whiteboards. For live sessions, post-its and large sheets of paper are still the most accessible.
We always recommend starting with individual thinking before bringing the group together, so group pressure doesn't influence the outcome.