1.Identify the KEY positions,
2.Identify the qualities reqd to fulfill that ROle.
3.Identify the likely successors,min 2 to 3 for each key role
4. assesmt centre is a reliable way to identify, but if it looks a costly affair,then put a rating/numbers to the qualities identified for the role & rate each of them as per the requirement sum total all the ratings,
the highest scorer is successor 1 ,
& the rest would be 2nd likely successor & so on.....