It's easy to forget how it felt getting our first tattoos- Intimidating. It can be nerve-wracking walking into a shop full of people who seem really tough, and thinking that nobody is going to want to listen to you or that you're going to screw something up. Although a lot has changed in recent years and the environment and culture around tattooing has changed a lot for the better, the first time can still be tough.
It can be difficult to understand why your client feels the need to explain their idea so thoroughly, but try and see it from their perspective; they want to make sure that you have a clear understanding of what they are looking for. Oftentimes, requesting too much detail can feel like a benefit because it FEELS like the artist has more direction.
If your first question, "What's the most important element of the tattoo?", doesn't immediately receive an answer, that's okay. You can gently push or press for one by mentioning something like: "We have to find a focal point in this design--a shape, idea, or element to draw attention. Everything else is just support material." Doing so gives some stern direction while still allowing the client to understand you're trying to work WITH them.
If the client isn't able to think of an answer right away you can tell them, "Let's revisit this in a week." This gives them some time to mull it over and figure out what is truly important to them. More often than not, they just needed a little guidance and they'll come back with a satisfactory response.
Now if they do come back with something substantial there are some questions you should always ask yourself: can this be a focal point, does it inspire me, am I able to visualize it? Sometimes, right off the bat, it will be clear. Other times, what they've returned with won't work. Just because they came up with something doesn't mean you're obligated to use it. If you don't think you can be creative with their ideas for the tattoo, then chances are good that your relationship with them as a client will become strained and stressful.