right, having worked on a farm for 3 years i've spent many a bored hour shooting tractors!
My advice would be:
watch out for distractions (licence plate, seat cover, window sticker + reflections)
use the lines of the tractor to draw the eye to the focus point, but either compose or crop so the focus point isn't centre frame!!
for this shot i'd suggest (we have an 8230 at work) standing on the steps and use look down the bonnet, use the curve of the bonnet to draw the eye into the 8330(2 in my case) sticker, and by using a long (ish, maybe 85mm on 1.6 crop 20d) focal length and the narrowest apperture (as low as you lens will go 2.8) you'll blur out any left over reflections. use the bonnet as a drawing line, yet include the background and try + get it as a sole colour, dark green of forests works as the contrast between the 2 shafes of green is good.
sorry if i seem to be trying to teach you to suck eggs, just sharing an idea