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Do you want a 100 websites that earn $1 each or do you want 5 that earn $20 each? The best advice here is to do as many as you alone can maintain. Too many and you cut yourself too thin and you'll not earn much.
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When you only have a few adsense sites you can add content and it be quality rather than trying to add crappy content to 100 sites.
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Having just one website leaves you with a dilemma if the site goes down the rankings. All eggs in one basket.
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Niche websites tend to work better than general websites. When you have a niche you can target specific words better.
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Bright ideas! A light-bulb moment; although rare (for me:)) are worth trying. If you have a good idea come back to this site and tell us about them.
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Don't try too much on one page. Don't for example try to get people to your web page for 'cooking' as a general term, when your page is optimized for 'curry dishes'. Add and extra page for each specific keyword term or phrase you're interested in.
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Remember this rule: Following the same theme. As people click on web pages they do so following a specific keyword phrase. Keep that keyword phrase as the main topic ALWAYS, otherwise you'll have them clicking the back button.
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Consider as an option to open new links onto a new page. There is some 'html' script to do this. If they are navigating through your site and click on an outbound like they are lost from your site forever; even when they've clicked on a adsense link. But when you've still got a page open in their browser there is a chance they'll return to your page and press another adsense ads.