When submitting my tutorials so sites such as Good-Tutorials.com or Pixel2Life.com, I have to think about image optimization because my tutorials won't be accept if the file size of my icon is too big. This topic has been posted in many places, but it is important so I thought I'd post it myself.

Image optimization is basically making a file as small as possible without losing a drastic amount of quality. I use Photoshop to optimize my images.

Simply go to File -> Save for Web

GIF will give the smallest file size, but also the least quality, so select it only if you have to.

JPEG is probably the best choice if you can go with it, it'll give a good quality image, and still a small file size. When using JPEG I like to make the quality around 30-40 for small icons, but around 60-70 should be fine aswell.