Pictures are worth a 1000 words. Here's a place I just Googled for sidegapping:

http://www.performanceunlimited.com/documents/plugsidegapping.html

You might also want to consider indexing your plugs. Here's a good article on that:

http://www.advanceautoparts.com/english/youcan/html/pht/pht20001001sp.html

Google for more on both subjects

"Never underestimate the power of human stupidity" - Robert Heinlein