If you haven't already, I'd recommend doing the Demonstration Setup, just so you can acquaint yourself with some of the basics of Munki:
For general troubleshooting, I'd recommend adding verbose flags to your output to see what's going on. If you need additional help understanding what's going on, posting back the output here (via copy and paste) is better than summarizing what's happening.
I will say if you're pushing an update, and it's a managed install that's an unattended install, it's very likely you won't see anything happen. Munki will try to install that item in the background without bothering the user.