My tips for you:
1/Draw things out before you make them. Initially onto paper. Make these drawings scaled and 2D. Then transfer these drawings into your CAD program. Have these drawings in both side and top view. Draw parts individually, but keep in mind the design as a whole. Make sure you are fully aware of regulations regarding a part before you start drawing.
2/'Box out' the regulations in your CAD program. This will help you come to modelling the parts.
3/Make sure your car 'makes sense'. I can see on yours the splitter doesnt join the sidepod. Look at many images of F1 cars to understand how the different parts join together to form a complete car.
4/Take your time, don't rush.
5/Work around a concept. Design your whole car around a principle, and work to achieve an aim.
6/Use mathematics to aid you. I see you're using sketchup. These two plugins should help a lot.
2D Fillet: http://www.ohyeahcad.com/download/
Bezier Curves: http://sketchup.google.com/intl/en/down ... ripts.html
Here is what I have managed in a very short space of time. Couldn't be asked to render it up. Very much a WIP.
Enjoy.