External Optimization deals with the points you should remember while promoting your website over web, the External world. This part of optimization effects not only ranking but has a powerful impact over the relevancy of ads too. This part of optimization takes time and your control over it is limited sometimes.
Anchor Text
Keywords in anchor text enhance the relevance of the target page with regard to the keywords used. You should build the relevance of each page of your site, through optimized anchor text containing important keywords, relevant to the theme of such pages, from other pages of your site.
Try to make link partners link you with the anchor text you specify (but please dont force them). The inclusion of important keywords in the anchor text can make a big difference in the final ranking as well as relevance of ads on your website. All search engines that matter give significant weight to the anchor text (both on your website as well as external websites linking to your pages).
Also, its a good idea to keep changing your Anchor text while running link development campaigns, the more varied options of title and description you have wider the coverage you get from search engines. Again, you can choose the keywords to use in your anchor text according to your choice between Traffic or payouts.
It is important to understand that as your Page Rank (PR) increases and resultant traffic increases Google may also increase your payouts. However, if you are getting highly untargeted traffic (or fraud traffic) your payouts automatically decrease with a period of time owing to phenomenon known as SMART PRICING. That is why Anchor Text is so important. Getting back links
The number of links incoming to your website may dont have direct impact over your Adsense ads relevancy. But The anchor text with which your link partners are linking to you are not only getting you direct traffic but also promoting your website to certain segment of traffic thats surfing on Search Engines.
When Targeted with wrong keywords resulting in wrong segment of traffic, it will decrease your CTR as well as your earnings potentially you could earn from that traffic. You can say, it affects the relevancy of your ads. This sounds weird but how do you define Relevancy of ads? Its defined as how much relevant or useful it is to the traffic coming to your webpages. isn't it? When the ads that Google is broadcasting isn't relevant or of interest to your traffic, its irrelevant. Promotion
To get the most relevant ads it is important that the links which you are getting from other websites should have proper anchor text. Your article gets prominence on the search engine owing to the relevant keyword used as anchor text. Even the links on your own pages should have relevant anchor text. This will help you get more targeted traffic and resultant higher revenue.
Other ways to promote your website is by getting inward links from free or paid sources, exchanging links from authority or important websites experiencing high traffic and leading in the Search Engine results (links placed at the top of the page get more importance, try for that) and there are many more things you can do to promote your website and earn more of Adsense money). 