The highest possible concentration in the domain name and or file name or subdirectory name.
The highest possible concentration (100%) of the <TITLE> tag and the main page title that people see.
100% of the <H1> tagged header if present, and lower proportions successively in <H2>, <H3> etc.
About 5 - 10% of the description tag - do not repeat the keyword more than one time.
At least once in the Keywords tag - it can be repeated in different phrases: EG Widgets, history of widget making,
widgets in China etc.
About 1-5% of the text, but not more. It is hard to see how you could make readable, normal looking text that had 10%
or 20% of the same keyword anyhow, but it might look OK to a search engine. If a human examines the text, and it says
"Overoptimization is bad" "Don't do SEO overoptimization," "Avoid overoptimization," ... in every sentence, they are going to draw obvious conclusions about
your attempt at "search engine optimization."
In most or all graphics alt tags, but not as 100% of the text in all of them.
In at least some of the title tags of internal and external links.
