I don't have a recipe but it's probably better to treat the client as a memmber of the team. They know their clients and what they want so just talking with them about that will offer you a lot of insights about the target audience.

Information architecture is another area where they can be part of the discussion too.

A nice new piece about this by Paul Boag: http://www.smashingmagazine.com/2014/12/30/designing-with-your-clients/

One thing I would recommend is a Co-design workshop session. I moved from a typical creative design agency to a service design agency 7 months ago and it has been a real eye opener. Pretty much every project involves the client/key stakeholders or customers as an extension of the design team. The co-design sessions are excellent at drawing out loads of ideas and concepts and there are loads of ways to run the sessions. Best concepts get taken forward/thrashed out in to sketches/wires/prototypes/visual design. These sessions do need to be planned right and facilitated correctly or you end up getting side tracked easily.

I would recommend this to any designer to experience first hand.

You could have your client focus on getting in the mindset of one who would use the app. This way they can (hopefully) start empathizing with the user more and understand your design decisions from that standpoint

Organize some meeting with your client during the project to help you build the product, don't just make him feel as he is part of the project, let him be a member of the project. I use paper or whiteboard drawing during these meetings to prototype the product with the client. .