For years, I believed my mission as a usability professional was to act as a user advocate. In fact, “User Champion” was once part of my official job title. At the risk of sounding sacrilegious, I now believe this concept is wrong-headed.
If you position yourself as an advocate for the user, you will often encounter resistance from the development team. They don't want to change course just because some self-proclaimed “user advocate” believes certain changes are necessary. They may not be convinced you're right; they may believe that they themselves know what customers really want. And they'll push back.
What's the solution? Easy. Rather than claiming to be an advocate for the user, be an advocate for the process. That is, the process of user-centered design, and/or the process of A/B and multivariate testing. When someone asks you (for example) how a new form should be laid out, you can say, “Let's test it and find out.”
Then you can run some usability tests (or some A/B tests, or whatever is appropriate) and find the correct answer. When you return armed with actual data, the development team will be much more enthusiastic about implementing your recommendations.
In sum, my tip for the day is this: Advocate for the process, not for the user. You'll go farther.