One of the big benefits of affiliate marketing is that you yourself can choose what advertisements you want to show on your sites. You can base the decision upon which pays the best and which is most relevant to your visitors. Regular advertising networks may show some ads that has nothing to do with your website just based previously visited websites of the user. Joining affiliate programs are free and quick. Some require that you have a site / blog up and running and a few require that you have a registered company. Mostly every online retailer and many service providers offers affiliate programs that can enable you to share profits with them, so almost no matter what you want to promote as an affiliate partner. Check out some of the best affiliate programs right here on Programorama.
Many or most retailers / online stores enable you to choose products from their assortment and promote. Perfect for for instance fashion bloggers that wants to write a post with their opinions about some new designer clothing and have relevant, useful and money making link straight to the product page within the store. This can be true for many different topics. A web design blog can link straight to the product page of the web design / theme that have been reviewed. A comparison website can extract and share the most crucial details and differences between offers and link to each option. Etc etc.
Choosing your own advertisements can also make your new blog post / magazine article have really relevant advertisements which can boost your earnings as well as the visitor experience of your site. Some webmasters make new websites or blogs based entirely upon a couple of affiliate programs or a category of programs they want to promote and write content for. So have I done and it can be profitable. Your own capability and investments of time, energy and some money is the only limit to how well it can be done. You can also get good ideas for new content that you can create by reading the details about the service, shop or products you want to be marketing.
If you are looking to add site wide ads you can compare and try out different ads by using a simple ad rotating script / code and see which is performing best and change the lowest earners until you find the best ads for your site. The best ads that will make you the most money may very well also be the most beneficial ones for your visitors.