Contribution drives direction. If you want to influence the direction of a project, roll up your sleeves and contribute in a meaningful way. The more ways you contribute, the better. Strive for a mixture of hard (e.g., code, prototypes) and soft (e.g., reviews, designs, ideas) contributions.
Over time, people will come to value your opinion as you demonstrate your passion and knowledge. You will become a thought leader according to your ability to demonstrate good judgment and consistently get things done.