Remember the old adage, "There is no 'I' in 'team'?" Apply that here. As a project manager, you are part of a larger team. A team, I'd like to remind you, that is involved because of their unique and needed skill sets. Don't just ask them for their insight during the project planning stage -- continually ask them. What you're looking to do here is to build their perceived investment. Because, when someone is invested in the outcome, they're more likely to go down the road of change with you.