You might think you're done pitching once you score an agent or get a publishing contract. The reality is once you have an actual book to sell, your elevator pitch is more important than ever.
As soon as someone learns you wrote a book their first question, every time, will be "What is it about?". You have ten seconds to wow them. Tops. If you fumble around for words or ramble for several minutes, you've effectively lost your audience and a potential reader or promoter of your work.
Instead, have a planned elevator pitch, two sentences max, that give the potential reader a taste of your book. Notice I didn't say the elevator pitch should summarize your book. That's not the point. The purpose of a pitch is to hook them into wanting to know more. They don't need to know your characters greatest struggle or how the love interest switch halfway through. They need to know why they should go pick up your book.
If you're read to take your pitch to the next level, consider tailored pitches. To use a tailored pitch you need to ask a qualifying question. It would go a little something like this:
Reader: So tell me what your book is about.
You: First, let me ask, what kind of books do you like to read?
Reader: Oh, I like science fiction/erotic romance/kitten stories/whatever.
You: Well, if you like (fill-in-the-blank), you'll love my book because...tailored pitch.
See what happened. You pre-qualified your reader. Instead of telling them about your book and hoping that's the kind of story they're into, you find out what they like first and then sell them on an aspect of your book that matches their interest.
This method of pitching also has the added bonus of engaging your potential reader in the conversation. Once you ask them a question, you start an honest dialogue instead of a sales pitch. This let's you get to know them and helps them discover why your book is perfect for them.
This won't always work. Someone who tells you they only read cozy mysteries is not going to be sold on your M/M romance. But they probably were never going to read your novel anyway. That doesn't mean you should dismiss them. Go ahead and tell them about your book. It might not be their cup of tea, but it could be perfect for their best friend/spouse/parent/kid/etc. You never know where you'll find readers.
Keep in mind that the WAM principle applies here. Readers want to know what they'll get out of reading your book. It's your job to show them why your novel will meet their needs.