you need to start higher poly, break it down into simple primitives: cubes, cylinders, ect. Pay attention to your silhouette it may also be helpful to work on half your model and mirror the mesh across.
Firstly, you are going to need a better reference image than that. Try and find something more head on, stay away from angled images. Look for pictures like this.
And like bunneh13 said, work in simple primitives and just use something like a symmetry modifier to copy over the second half of your model.
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Hopefully this image will help.
http://i.imgur.com/dL1uAGa.png
And like bunneh13 said, work in simple primitives and just use something like a symmetry modifier to copy over the second half of your model.