I think it helps a lot when you start from the position that everyone has the right on his own “handicaps”, the weak points so you will… The main pitfall for most managers is to hire people based on their strengths. You are really happy with the new recruit and after a couple of months / years you might observe some points which you still miss to make him or her Mr. or Mrs. Perfect. You step into the challenge to develop these points as well and as a consequence the new recruit might lose his strength while trying to develop those weak points, which at the maximum might become just average. As you understand a waste of strengths and potential.
So after embracing that everyone has the right to have some handicaps, some weak points, or even something edgy you are ready to start looking for the real strengths and how to develop these further. The easiest way is for sure with starting to ask open questions:
What do you see as your real strengths, your core qualities?
What makes you special?
How and where would you further develop these strengthts to the benefit of yourself / the company / the department / the team?
Another way could be asking the colleagues, what do they see as a special strength? And last but not least… for what special task / challenge would you choose to work with this person?
All the answers will give you a good indication of the strengths which hold so much future beauties.