Something that i started to do recently was to target two or even three keywords in my articles i submit to www.ezinearticles.com. It has really driven more traffic to my Adsense pages more then a single keyword article ever could.
To do this i go the the free Google keyword tool and find my first keyword. I shoot for medium competition with this keyword with under 20,000 competing pages when searched in quotes
The next keyword i try for slightly less so maybe 10,000 competing pages when searched in quotes.
I will then use these two keywords in the title and try and keep the keyword density the same for each keyword. I like to keep it at 1-1.5%
I put the keyword with the most search competition first in the title.
The results have been literally amazing, the article traffic has doubled and my earnings got a slight bump. Plus it is very easy to do. I am currently going back over some old articles t modify them in this manner.
I wish i had started doing this when i first started article marketing and for the life of me I cannot figure out why i didn't?