Create a new document with settings for example 3000 pixels wide X 2300 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 two perspective lines as it is presented on a picture.
In this tutorial I decided to draw Maserati Zagato A6. If you still don't feel good in sketching, for practicing purposes I suggest to use one of the reference photos of this model. Start sketching a car.
Here is just a simple example how to draw wheels. The basic thing is to keep the ellipses in correct position to the perspective lines. Also, as I showed on the picture, there are 3 size-different ellipses that creates a basic shape of the wheel.
Pick up dark grey color and add some more details to the cockpit. To do that you can simply use the same method as before: 1. apply a color, 2. erase unnecessary elements. Shape it and create a depth.
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.
Save current project to jpg format. Next select the file from the folder you have saved the jpg image and drag it into the Photoshop program (in to the same document). Place the layer with the image at the top and select: Edit --> Transform --> Flip Vertical. Drag and drop the bottom of the car just like in the picture.
Select the layer with jpg file. Click the button "Create a layer mask" --> select the Gradient tool --> set the gradient to: White to transparent. After that simply drag the mouse from the bottom to the top of the vehicle and create the effect imitating a reflection on the floor.