Coaching is about helping people improve both individually and as a team. But there's more to coaching than just walking around and answering questions.
Agile teams value methods, methodologies, and frameworks (like Scrum) because they're really useful. But we value individuals and interactions over processes and tools. That means the most important thing methods and frameworks do for our teams is to help the people on them work together in an effective way.
Even when practices seem to be technical and focused on project management or engineering, at their root they're about people. Iteration, for example, is about learning as a team about the product you're building, and about how you'll build it. Refactoring is about making the code easier for people to understand, maintain, and extend.
Listening is the difference between a Daily Scrum and yet another boring status meeting.
Documentation—from project plans to user stories to code comments—is about people. What I wrote on this piece of paper (or JIRA, etc.) isn't what's important. What's important is that what's in your head matches in my head. The paper is just a tool to get us there.
Good ideas come from everywhere. Listen to your junior developers. If your team has a diversity problem (e.g. not enough diversity, understanding, or tolerance on the team of people different than them), that's often related to a deeper listening and learning problem that can seriously affect performance.
So really help a team—as a coach or a team member—you need to understand how and why the method they use works, both in theory and in their day-to-day work. That's one of the biggest challenges of agile coaching.