One on the main differences in being a amateur and pro is what you do after you take a photo. Most amateurs just print their photos while pros will touch up or manipulate their shots. Photoshop is the king of all digital manipulation programs. You can buy Photoshop CS4 on ebay for around 200 Dollars. So, If you want your photos to look more professional you should learn photoshop or a similar program.
I found this short video on how to vignette a photograph online. Try it out and see if it adds a spark to your photos! Enjoy!
Cropping in image can be very important if you plan on printing a photo. What you see in your camera is not what you get when you print a photo. A 5x7 will need a different crop than an 8x10. To help out I have found a video that should be useful.