Do NOT start with the code. Being a developer, this is really hard to say. jQuery Mobile is very fast and easy. Refactoring is also very fast. However, there is something that happens when you jump right into HTML prototyping.
People who don't know code will assume that we're much closer to a complete product than we actually may be. This is especially true with jQuery Mobile because even the most rudimentary stab at a project comes out looking polished and complete.
People will start to fixate on minutia like spacing, margins, colors, logo size, and so on.
Due to the sunk cost of our time in the current design, we are less likely to make significant changes from whatever we initial coded because refactoring is easier than a do-over.
Instead, get a pen and paper. Wait, what? Isn't this a web developer book? Relax, you don't have to be an artist. Trust the process. There will be plenty of opportunities to code later. For now, we are going to draw our first jQuery Mobile site.
The great thing about starting with paper-based ideation is:
We are more willing to simply throw out a drawing that took less than 30 seconds to create
Actually sketching by hand uses a different part of the brain and unlocks our creative centers
We can come up with three completely different designs in the time it takes to create one HTML page
Everyone can contribute their best ideas even if they're not skilled in graphic design or coding
We will naturally begin by drawing the most important things first
More attention is paid to the ideas and flows that actually make our site work instead of the myriad details, which few would even notice
We will probably end up with a more user-centered design since we're drawing what we would actually want
Ideally, 3x5 Post-its notes are perfect because we can easily lay them out on walls or tables to simulate site structure or process flows. We could even use them to conduct usability testing. A little later, we'll lay out our drawing for the owner to see how the whole thing could work before we get buyoff.