I want to open up more sites, but what's a good way to link them from my existing sites? If I put it in the header, will that they away from my adsense revenue?
Well, it depend how related the sites are. Yes, some people may click on to another of your sites instead of adsense, but then you have a chance that they will click on an ad on the other site.
Agree. It totally depends on your site and what site you want to link to. Actually there are tons of variables. Is it related? What type of site? blog, directory, ect Are the ads on the new site paying more per click? List can go on.
Does the site have the be related? If yes, how much related must they be? Like if I am talking about computers, can I talk about video games, stuff like that?