Chutzpah goes very far. Ask for what you want, and explain why you deserve to get it -- then offer to demonstrate your fitness. It's an excellent approach!
Chutzpah's critical though- you're usually not going to get what you want if you never ask for it. You can wait a really long time for people to just give you what you want, especially if you never express an interest by asking for it.
It sounds like common sense, but it feels like it took about 20 years too long for that to really sink in with me. I always assumed people understood me a lot more than they actually did.