Create a new document with settings 1600 pixels wide X 1200 pixels high. From the tool palette, select the Brush Tool (B), and then select the icon: "Pressure", thanks to that the pen tablet will respond to your pressure so as to obtain a smooth line brush. In the settings, choose size "3" tip hard. In the tab "Layers": double-click on the first layer (Background). Draw a sketch of your concept car.
Continue sketching. Think and design pattern of the wheels. To facilitate the work, you can draw a pattern on one wheel first, then copy and move them to the rear. When the sketch is finished, removed completely unnecessary lines (eg, those that go beyond the "body" of the vehicle}.
From the color palette, choose a slightly darker shade of the same color as before, (in this case it's: #E0C822). Choose a soft brush and set the size to 100, opacity 15%. Create a new layer. Apply the color to the "body" of the car. Remove unnecessary brush strokes.
Create a new layer. Choose black color from the color palette. Select a tool "Ellipse". From the options bar, select "Shape" and while holding the SHIFT key, draw a circle. Using the Shape option, the path of the wheels will be created automatically, which can be used in the later stages.
Create a new layer. Choose black color #000000. Set the brush size of 3-5 and opacity of 100%. Draw the rim cavity, as in the picture. To make it easier for you, the wheels can create a selection. So you do not go beyond the selection brush.
Create a group of layers. Move all the layers containing the elements of the front wheel to this group. Copy group and while holding down Shift key, drag a copy to the rear so you will have second wheel in the back. Create bottom black shadow under the car using black color #000000.
Create a new layer. From the color palette, select lighter color than the color of the current window (in this case, it is a gray color). Select the Pen tool (P) and shape into a path that will mimic the glass on the other side of the car. In the "Path" tab, click on the button "Fill Path color". Add more details on the side.
Now add the first shades to the car body. For this purpose is necessary to create a new layer. Move it under layers with the wheels but before the layer contains main color of the car body. From the color palette, choose a slightly darker color (it is a: #DABD01). To impose this color I used the brush: "Square (coal)"
From the color palette, choose a much darker color than the main color (#473c00). Select a brush with a soft tip, or brush, called the Square (coal), size 100, opacity 10-20%. Apply the color until you are satisfied with your shadow. Remove unnecessary brush strokes using the Eraser tool with a soft tip and set the order of 20-40% transparency. Do the same thing as above but using much lighter color. This gives you intense reflection of the body.
In this stage, I want to show how to perform a smooth transition of color tones. First select the decidedly darker shade of the main color. Choose the brush tip: Square (coal) and set the size 40-50, with 25-30% opacity. Apply a layer to the car body.
Now select the Eraser tool with a soft tip and set the parameters for: size - 100, opacity 10-15%. Then start removing one part of the film, creating a smooth transition from darker to lighter. Look carefully at your project and think where else you can add or enhance the shadows. If you find such places - apply them there.
Continue sketching and add more details to the car mirror. To create lines defining the shape of the door or door handle, use the Pen tool and create a path. Next, set brush tool size at 3 and opacity to 100%. Go to "Path" tab, and click on the "Stroke path with brush" Of course you can do it manually however, make it possible to adjust the path of the line in case of committing any errors. In the same way add lighter lines slightly displaced from the previous one, so that the effect of the cavity is obtained.
We're going back to the wheels for a moment. On a new layer in the layer group (wheels), add a clear reflection of light brown color at the top of the tire and shadow on the bottom. Erase unnecessary parts. In addition to better effect, you can add the grooves in the tire.
On a new layer create a path like in the image and then go to "Path" tab and click the button "Load path as a selection". From the color palette, select a white color. Set the opacity of 80% and size of 70-100. Paint over the top of the selection creating intense reflection on a glass.