I was recently asked the following question.

Try using "position preference". You can set it to only allow ads in the #1 position, which should be the "green area". Adwords will manage the CPC so that your ads appear only in that position. You can limit the daily budget to control costs.

Read more about position preference from Google themselves

http://adwords.google.com/support/aw/bin/answer.py?hl=en&answer=36482

Google has not released any information regarding acceptable keyword density. But, the accepted theory is that your maximum keyword density is 5%. That means if you have 200 words on your landing page, no more than 10 of them should be the keyword. Five percent is a high density and it's difficult to exceed that mark.

I generally look for a keyword density anywhere between 2% and 5%. That range is assumed to be good for Google SEO and Google Adwords.

I tend to make sure my keyword appears...

1. in the page url
2. in the page title
3. in the meta description and meta keyword tags
4. in the h1 tags

If I've done all four of the those, I find that I can have naturally written content without concern for keyword density and still get good quality scores.

The following is an email I sent to Marshall Alder who has been having trouble with One Week Marketing from PotPieGirl.

I think the methods may work, but you really have to get into the long tail keywords. Did you get the Bum Marketing course from Travis? It talks about finding the right long tail keywords which I think is half the battle.

http://www.bummarketingmethod.com/

I agree with Travis and before I ever read his materials, I was using The Google Keyword Tool and plain old Google Search Results to conduct my research. It's all free. In a nutshell here it is...

1) Find a product. PotPieGirl says find either a market or a product, but I personally start with a product. I do think cb-analytics.com is a good place to go, because clickbanks marketplace is hard to navigate. I also like CommissionJunction.com, but let's stick with ClickBank.

Now, I think the product has to have some gravity. Gravity indicates that somebody is making sales. That means there is a market. Plus the sales letter has to be doing its job if other affiliates make money. Of course too much gravity may mean there's already a ton of affiliates out there. I'm really still trying to define a good gravity point, I'd recommend 50 for now.

http://www.cb-analytics.com/

2) Take a main keyword for the product or the primary market and go to the google keyword tool, and pull up all the related keywords. Look for keyword that have about 1000, maybe even 2000 global monthly searches. Any more than this and there probably too much competition. Of course, you never know until you look, so give a few higher volume ones a try. Find ten long tail keywords that you will research further.

https://adwords.google.com/select/KeywordToolExternal

3) go to plain old Google.com and search for your ten keywords. Wrap each one in double quotes, do a search and see how many pages returned there are (this is called "phrase" match). Travis says you want keywords with less than 1000 competing pages. I agree.

Hopefully, 5 of your 10 keywords fit the 1000 or less competing pages rules. If not, go back to the keyword tool and get another 10 keywords, and look at the competition for them.

4) After you have 5 low competition keywords, start building your Squidoo lenses, writing articles, everything PotPieGirl recommends.

Again, I think if you put more into the keyword research, you get more out.