Effective use of xpath in automation (Recursive Descent Xpath)

using xpath in the automation can let you down any time. so there is a big question what do we do when there is no option left except using xpath. so we have recursive descent xpath.it actually search for particular context element.
for example:




following is the description of recursive descent xpath from Microsoft:

An expression that uses the double forward slash (//) indicates a search that can include zero or more levels of hierarchy. When this operator appears at the beginning of the pattern, the context is relative to the root of the document.For example,
the following expression refers to all elements anywhere within the current document: