Pay attention to the task at hand - a brewery is a dangerous place. Follow checklists for tasks to make sure you don't miss anything. Learn what is top priority, and if you don't know ask. You're never done working, just done for the day. There will always be other stuff to do.
Also, pay attention to not just what the brewer says, but what he/she does. If the brewer skimps on important stuff, you might not want to remember too much of what you learn. I know of one local brewery who will not hire people who have ever worked at another local brewery . . . wrong mindset, bad habits, etc.