Practically in the shadow of this amazing geological feate, Diamond Head, I listened to an excellent lecture by author and communication/creativity consultant, Sam Horn. She answered the question of what to say when people ask, 'what's your book about?'. If you ever get the chance to see this lady speak do it, she is compelling.
'First she said, don't tell what your book is about, tease them to incite curiosity and interest'.
If you ramble on then they will tune you out and you'll have lost them. The worst thing you can do it bore people. If they start to get that faraway look in their eyes or keep glancing around for exits, you're talking too much and not engaging them.
'Don't explain your book, ask them something to turn it into dialogue'. A statement leads to a dead end, while a question leads to a conversation.
'Don't do run on rhetoric, give a real life example using imagine or 'have you ever' type of questions'. This gets them to relate to your story in some small way.
'Don't confuse them, finish with an airtight sound byte'. Give words that have a rhythm of rhyme, something memorable. Make it memorable!
'Don't lecture, but do link your project to something familiar or fond'. What book, novel, or author are you like? Be careful when doing comparisons though, an agent or editor may also want to know what's unique about your project (my words).
This is only a fraction of Sam's advice, forty five minutes wasn't nearly enough time to cover everything in her amazing repertoire. For more of Sam's invaluable advice check out her website, it may just help launch your career!