Upload & Sell: Off
I also have been experimenting with LR4 to kind of get an idea of the processing aspect of things before I jump into PS.
LR is a really good tool, often underestimated, and you should really master it IMO before worrying about photoshop... my major complaint about post processing is the amount of time it will rob out of your life per image, so I'd advise you to stick to lightroom until it takes you no more than a couple minutes to adjust each image you import, save those exceptions you really want to do something special about (those will always be time consuming, but will be that much more rewarding as well).
Anyway, this is a cropduster that me and my girlfriend chased down in Central Illinois this summer. This is one of the handful pics I have had time to process in LR4. It was shot in jpeg and I am now shooting in RAW. C&C would be greatly appreciated. Feel free to take it and run with it and show me the way.
As most already pointed out, color saturation seems a bit too much - unless that's really on purpose, it should be tweaked out. Other than that, your cropping could be tweaked. Here's yet another view on your image - as you can see, there are plenty of ways to do it, and each one of us tweaked it accordingly to a particular interpretation of your original image. It really depends on what your vision for the image is, and your post-processing efforts should always focus on bringing the image closer to your vision.