Self-advocacy in the music biz can be challenging, and I'm often asked my approach to negotiating, etc. I could write ten thousand words on the subject, but here’re five things I try to keep in mind:

Know you’re worth it. The world needs your art, your story, and you deserve fair treatment. Don’t let anyone tell you differently.
Get the facts. Ask around. Have friends been through something similar? Check the accuracy of every claim, and don’t leap to conclusions. I remind myself that the folks sitting across the table are in the music industry too, which means they also have no idea what’s going on. Try to understand the situation from their perspective, and strive towards middle ground.
Express yourself clearly. Take time drafting emails, be brief, and don’t allow yourself to be diverted or ramble with unimportant details.
Assert yourself clearly. Don’t lose your temper, lash out at the other person, or attack their character or organization. Speak out, ask for what you want, and listen. Respect the rights of others, but make sure your voice is heard.
Be firm and persistent. Keep after what you want and follow through on what you say. Developing a think skin’s particularly difficult for us sensitive types, but it comes with practice. Stand strong. See point #1.