The photo has some very strong vertical, horizontal and diagonal thrusts to it, and that's what I'd like to emphasize in the painting. The first step is sketching in the main elements. This is all done rather loosely. If you're not exact with the pencil, that's fine. You want your final decisions to be made with the brush. It makes for a much fresher painting when you're not filling in the lines, but making the definitive shapes with the paint.
Now we place the initial washes. The paper's dry and the brush is wet. Where ever you stop painting you get a hard edge. Start at the top and work your way down. That way you have a leading edge of wetness at the bottom as you add to the wash. Think overall shape. A vignette was in the back of my mind the whole time, and that helped me with the design of the shape. Burnt sienna and cobalt blue are a magic combination that when mixed just right make a perfectly neutral grey. The key is to not mix it just right, but have some parts dominated by the burnt sienna and some by the cobalt blue. The brown streak in the front of the train is one of those happy accidents that you leave alone that shouts "rust". This is Cleveland after all! And make sure you leave anything that needs to white dry. You can see I left the strong highlight on the train and some of the crossbar of the power line support white.
The over all shape is defined, but the washes within are all soft and murky. It adds to the mystery.
The overall wash is mostly dry now (at least the upper parts of it are. The easel is set at about a 20º degree angle, allowing the wash to drip down. This allows the moisture to collect where ever there's a hard edge at the bottom of the wash). Darker colors are added. Since the top was dry, I added the background wash against the station and the one facet of the building. You can see that the strong vertical, horizontal and diagonal thrusts are being played up. Then darker washes are placed in foliage area so we can see the power line supports and some wires start to take shape.
Here it's just about done. As far as looseness goes, I like the previous stage the best, but you've got to have a bit more recognizable elements in there to make it read as a scene. Try to design it. Don't make any window identical to another window. Think variety!!!! As the great watercolorist Tony Couch says, "you're job is to entertain the viewer." You do it through repetition of similar shapes, and a variety of those same shapes and the spacing of them.
And here it is finished, with just a couple more darks placed under the train and a little more definition to the shelter on the train platform.
It's mostly a study in design. Think simple shapes and minimal detail.