

Here is my advice (and I am not that good, so take it with a grain of salt):
1. When framing the shot, try to catch the bikes either coming at you, or parallel to you for a more striking shot
2. Also, when photographing a moving object (car, bike, person, animal, etc.), you should place the object to one side so that when you look at the pic, there is some room in the frame for them to move into
3. Focus seems off; try panning to get the subjects in focus
4. Not sure on this one, but overall image looks red. Could be the dirt is really clay, though, as the blue in the sky and the green bike seem OK...
The most important thing (geting out and experimenting) you are already doing. Now try to shoot from different angles, with different appertures, ISO and shutter speeds... Hope this helps!