First, I read the client's article and research the topic at hand. This is a good opportunity for me to immerse myself in the article subject. Doing so allows better understanding of the article so the end product is well-rounded and closer to what the client is envisioning.
I then create a number of thumbnail sketches to get a general idea of the layout. These are very loose sketches just to figure out the composition for major parts of the illustration.
Once I choose the best thumbnail, I start collecting my references. These are usually photos I take myself or a mixture of stock photos and my own photos. I then create rough, preliminary line art with two color choices for the client to decide between. If the client requests more than 2 color options, it is discussed before the budget is decided.
After the client chooses which color option they like best, I begin the final piece. I start with taking the line art I created for the color choices and enlarging it to the scale requested by the client. I then re-draw the line art so it's more precise and clean. My price allows for two modifications to the illustration before submission.
I start with traditional media, using ink and a brush for the line art then scan the work and finish the piece using a mix of the iPad and the computer.