I started by creating a poly plane, rotated it to match the front of the car and then scaled it to cover the image plane. I then extruded the plane back to create a box large enough to contain the vehicle.
I then added edge loops in key places, for example, on the edge of the wheel arches, bottom of the windscreen, the top of the boot and then one sideways along the length of the box. I moved the vertices and edges to roughly match the shape of the car.
At this point, it was mostly adding edge loops and deformations to get the model matching the images used as reference.
To create the wheel arches I roughly shaped them using the vertices closest to the the edge of the arch. Once the shape was satisfactory I deleted the polygons inside the shape and the ones beneath the car connected to them.
I then shaped each polygon individually, extruding the edges and then placed them to create the actual arch. I then merged the vertices together to stitch the model back together.