Not to put too fine a point on it, but well, duh. A trusted advisor relationship will not be created by passively responding to client issues and questions. That is transactional, and while occasionally, I might exchange a transactional email or two with clients, my goal is always to elevate those relationships to be, in general, something more. I strive to be a partner, an advocate, an advisor.
Not every client wants that relationship, to be sure. I need to determine what is important to the client (goals, keeping their own boss happy, successful and measurable outcomes, etc.), and ensure I align with as many of those things as I can.
A client who keeps me at arm's length is just a partnership waiting to happen. It's my job to figure out how.
This one is a little trickier. There is a balance to be found between being honest and dragging all the skeletons out of every closet for the world to see. Finding that balance is the first step.
Then, I align myself with how the client is likely feeling about whatever topic is under discussion, and responding in a way that is real, in a way that is human. If their experience was terrible, I will acknowledge that, and then move on to solutions, but only once the client has had their say. If they need to vent, I need to listen.
See above re: aligning myself with how the client is feeling. There is nothing worse than feeling as though the person on the other side does not understand your position. By starting from a place of empathy, I can de-escalate a "hot" situation more quickly, and progress to solutions faster, as well.
Being proactive, authentic, and leading with empathy have garnered some of the most rewarding client relationships of my career.