Let's Talk: Photo Cropping

Remember this photograph? I posted it here, as a potential selection for my January Photo-Heart Connection. At the time, I promised to talk more about the photograph and the young man in it.  He's one of the other seniors on Henry's soccer team and holds a special place in my heart because he's the only other one who has played soccer all four years with Henry. When they were freshman, the program was in a bit of disarray so no one else went out for the team. This year, they're both Captains and the team is thriving. He is also just a terrific kid - polite, hard working, responsible.  His older brother was the first one in the family to go to college, and we're hoping that Andres follows in his footsteps. 
As for the photograph, I love it because it emerged during processing from this original:

On Senior's Night, we give a nice framed action photo to the seniors as a going-away gift. Since I'm responsible for this task, I shoot lots of photos of the seniors during the season to try to capture something special.  I took this picture of Andres walking off during half-time. Although I liked his expression, I thought it was an unremarkable photograph.  But when I cropped it using the rule of thirds (and brightened it up a bit), I ended up with a photograph that I loved. By placing him in the left third of the frame, rather than in the center, he becomes the focal point. I've left enough of the soccer goal to give context and the depth of field is just right (background soft, but not blurry). I'm really happy with how it turned out. 
Usually, I try to frame my photographs while I'm taking them, so that I don't need to crop them in my computer. For action shots, though, I usually don't have that luxury. That's when cropping on the computer really helps.
What about you? Do you crop photographs on the computer? Or compose them correctly in the first place? Do you think about design rules (like the rule of thirds) when cropping or just play around until you find something you like? Got any other cropping tips to share? Let's talk about it . . .
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"Let's Talk" is a semi-regular series designed to inspire frank discussion and sharing of information on issues relating to photography, art and blogging.