I was told that this were bonuses, and raises are "negotiated".
How can I prepare to optimize the outcome to my benefit?
If your employer publishes criteria for different levels, try to aim your evaluation to hit the responsibilities of your current and next level.
It's best to start this process as an ongoing discussion with your manager and ask them what you'll need to do to get a high mark or a promotion and track your progress against the goals you develop together.
Beyond that, the review should just be happy talk and "Keep up the good work!".
Anything negative, move on. Want a raise, move on.