Arranging the images in the sprite horizontally as opposed to vertically usually results in a smaller file size.
Combining similar colors in a sprite helps you keep the color count low, ideally under 256 colors so to fit in a PNG8.
"Be mobile-friendly" and don't leave big gaps between the images in a sprite. This doesn't affect the file size as much
but requires less memory for the user agent to decompress the image into a pixel map.
100x100 image is 10 thousand pixels, where 1000x1000 is 1 million pixels
1More
New Yahoo Mobile Development Suite for App Makers - 0 views
1More
YQL: Using Web Content For Non-Programmers - Smashing Magazine - 4 views
1More
Apple and FireFox ditching Google as its default search engine - 0 views
1More