Speaking Up

When should we speak up to those in power? I have no problem speaking against those who are abstractly in power, largely in power, and far away while in power. But I'm struggling with how to speak up to someone who is actually in power over me. That is to say, someone who has direct power to say whether I get to earn an income or not, whether I get to maintain my professional relationships or not.

I'm not talking about starting a revolution. I'm not talking about being rude or threatening. I just want to speak to someone about how I assess my own work without kissing their ass in the process. Is this pride/defensiveness or professional integrity?

It is important to show respect to those who have more experience and take the thoughtful suggestions of those who have been doing the work a lot longer, so when so I speak up?