The problem could be initially intimidating if you've never heard of the term lowest common ancestor. However, once you realize that it's just the highest shared parent that two nodes have in common, it's easy to visualize ways to use some form of traversal to our advantage.

One way to go about this problem is to visualize the traversal path required from the leaves. We'd probably want to move towards the top since that's where the ancestor is. In other words, we would follow the nodes upwards to get to the lowest common ancestor. This means if we wanted to find the LCA of 2 and 9 below, we'd first trace 2 upwards (so the path followed goes 2 -> 4 -> 6).

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/*

       6 

      / \ 

     4   9 

    / \

   2   5

  / \

 1   3

*/