If you have the ability to do so, watch your users USE your software. Talk to them while they do it. Have a real conversation about their work and how your software enables (or not) them. There's nothing better.
I just spent 2 days in our lab just wandering around with no agenda watching, talking, joking, empathizing, and mostly listening. I came out of it with a way better understanding of what's going on with the system than I ever could have otherwise. I came out of it with way more bug reports and feature requests than I would have in 3 months of passively waiting for the user to ask. I came out of it better able to serve my customers.
When you can, leave your office, get out among the people, and just be a guy walking around looking and talking. It will do wonders.