It's true, tiny pocket robots are becoming more powerful.

You'll need three things:

The right app - I'm currently using the Slow Shutter Cam app for iPhone. Sure there are other apps, but as of right now, this one's by far the best. Easy to use. Great design.
A steady phone - Highly recommend the Glif tripod mount. You can also try balancing your phone on something solid, but it might limit your ability to frame the photo, let alone tap the screen without moving it.
Patience - Rocks excel at this. Girlfriends being attacked by gnats do not. Though, as you'll see, she did a top notch job standing still considering the circumstances.

It may also take a bit of pride-swallowing while your dinky phone sits atop a huge tripod. But the result's probably worth it:

Now compare those to this behind-the-scenes shot, taken at normal exposure with your standard point-n-shoot...