- Include an invite for a quick 10-15 minute chat in the welcome email (more people than you would think actually take up the offer)
- Ask them why they signed up (this is key to help you determine what problem people want you to solve)
- Ask them their biggest frustrations about the solution so far
And just take it from there.
Processing existing customer feedback has always been a problem even at large, established places I've worked for - chasing the new customer and adding features is always sexier than a general feeling of unease that requires a lot of prying to get to the root of.
Often in my experience most customers don't seem to know what the exact problem is, or can't put it into words, so having strategies to tease that out would also be appreciated.
If you have nothing to go off of but a rough sense of which part of their day is causing them frustration, you can ask "I heard that (process X) is hard or frustrating. Can you walk me through how that works? Where does it start?" followed by very simple questions to keep them talking - they'll get as detailed as they can for someone who appears to be in a position to help.
I might meet to chat for 10 minutes but if you told me you'd give me a $5 (or even $50) gift card in exchange for my time, I probably wouldn't.