Then ask them! "Hey guys, I'd really appreciate some feedback on how to improve. I won't get defensive and could really use your advice -- please be honest!" This can go a really long way.
It's always a good idea to ask for feedback in a thoughtful way, put people at ease, and communicate that they won't have to deal with emotional fallout. When people do that, I always take the time to give good feedback. If people still give you a BS response after that, they're just jerks and you shouldn't be paying attention to their feedback anyway, even if you got it out of them.
