I have not been paid nor am I associated to any of the products outlined in this guide. These are simply the ones that I use. There are many alternatives than you can or may already be using.
A sturdy tripod is a must. I use the Joby Gorillapod with their ball head. The iPhone bracket is a cheap plastic number, bought from a renowned online auction site.
Next purchase Slow Shutter Cam App from Cogitap Software Developer on the App Store.
The app has some great options to shoot in automatic and manual mode, and also take long exposure and light trails. This guide is based on using long exposure.
Next, setup shot and frame. This image is Eastbourne Pier, Sussex. (image copyright steve angelkov)
Within slow shutter app, click on the lens icon in bottom left hand corner and select automatic from capture mode and B for Bulb on Shutter Speed.
I chose bulb mode as I wanted a long capture for movement in the water, but you can choose shorter shutter speeds, for different subjects.
In bulb mode, just click to take photo and click again to stop capture. I selected 16 seconds. As automatic mode is selected exposure is spot on and captured in camera.
Once the photo is captured, and you are happy, you can save to camera roll. N.B. the app has 3 settings to save, make sure you have selected large, which is available for iPhone 4, 4s & 5.
Within the app their are some excellent instructions and guides on how to use it.
Next, open snapseed to edit into black and white. Select Black and White from the options at the bottom.
Click on the star in the bottom toolbar, and select the chosen B&W profile. I chose Neutral, but others are: contrast, bright, dark, film and darken sky. (image copyright steve angelkov)
Next, click on the filter icon to select from: neutral, red, orange, yellow or green. I chose yellow. Click to save. (image copyright steve angelkov)
Here is the finished image. (image copyright steve angelkov)