What sorts of information do you require in your sign up flow? Right now I'm just collecting name and email but want to add phone number and maybe a few others to help me follow-up. Has anyone experimented with dropoff rates and whether it makes sense to ask for additional fields such as phone number in a separate step after you've collected email in the sign up flow?
In my experience the more the user feels forced to provide what they feel is personal information the less likely they are to sign up (although depending on what you're registering them for it may not have large impact).
Perhaps try to employ a system where it guides / entices users to fill out their profile? Like a point system type of things. Even if the points don't really mean anything it's a gratification thing that might have users pony up more information. (Think about how sites show you what % you are in completing your profile. It's one of the human natures to get that up to 100% just because)