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There are many other variables which affect earnings though. Some will earn as much with a thousand visitors as others do with tens of thousands, thanks to a high paying niche, a targeted website and the fact that Google is playing ball with them (in terms of things like SE listings and smart pricing).
1) Very interested in your topic.
2) Find ads on your pages related to what they are looking for.
3) Can afford to subscribe or buy online, or whatever your advertisers are expecting them to do.
4) Are patient enough to stay on page and not randomly click left and right in seconds.
5) Will bookmark your pages.
6) Will tell friends about your pages.
7) Will add a link to your site if they own a web site.
You get the point, it all depends on the amount of work you put in developing your pages, and the end product quality and audience acceptance, no one factor can give you those, and even all factors cannot guarantee getting those, just do your best within what you can control on your pages and leave the rest to Luck & Google.
Six things to remember about advertising income
1) 1,000 uniques a day does not equal $1,000 a month. I've got one site that hit a level of around 3,000 uniques a day the past month, yet this site only earns around $100 a month (one hundred).
2) Not every visitor will click an ad. Even with relevant ads, like adsense, not every visitor will click an ad. Far from it. A click-rate around half a percent is not unusually low. That's fairly standard. That is: Show 1,000 ads and get five (5!) clicks.
3) Not every ad pays the same amount. Some ads cost less than a dollar for the advertiser, some cost several dollars. It's all about demand - the more demand there is for ads on some topic, the higher the price.
4) The higher the ad price, the higher the competition. Yeah. all the other webmasters here "figure it out" as well. Well, at least they add two and two and it makes four. So, they chase the exact same words you do. And there are more of them than the one you. Meaning: It's pretty hard to get to rank for any of that stuff unless you do so in advance.
5) You don't get all the cash. What you get when somebody clicks an ad is around 50%-80% of what the advertiser pays. Google (or the other networks) pockets the rest.
6) The kind of traffic is more important than the number. Some sites will be able to make $1,000 monthly out of 1,000 daily visitors. Others will need 10,000 or more to make $1,000 monthly.
I think that sums up the most important points. IMHO, YMMV, AFAIK, FWIW, etc.