Aspect Ratios. This isn’t a particularly deep or sophisticated byte of knowledge, but I never really sat down to learn it, resulting in some irritation when I enlarged photos only to find the printer has cropped the image, making it unbalanced. If you’re shooting with a DSLR or point-and-shoot, your aspect ratio is 2x3. That’s how your sensor captures the image. Thus your standard 4x6 print always looks right. If you don’t crop the image in your post processing, this means you should enlarge your prints to the following sizes:
One thing to remember is that if you’re taking a photo for someone else (a client), and they want to enlarge it, they’re most likely to make it an 8x10. For no good reason, that’s a standard size for photo frames. So you have a choice: either shoot with extra room on the width of the photo, or educate them on how to buy the right frame.