Make sure you place the ad correctly. Ads that people can’t see won’t be clicked on, so make sure the ads are located in a prime spot that will generate interest. The best spots for an ad is on the top fold of the webpage, meaning the viewer can see the ad without having to scroll. But not on the very top, most people don't look there
Consider linking text. This helps to make the ad stand out more and gives a better chance for the viewer to actually read the ads. Secondly, since the ads are embedded within the text, it’s harder for the viewer to miss. Ads located on the sides are oftentimes looked over, which is exactly what you don't want visitors to do.
Put small, relevant images next to your ads. This has been show to increase ad revenue because this attracts attention to the ads, and people are tricked into thinking that the picture is content related to the ad. Google Adsense allows this method (somewhat, however, some images placed next to ads can violate Google TOS, ask Google before adding images next to ads), however Yahoo Publisher Network does not allow it. Read the TOS on certain publishers to get more info on whether this is allowed or not.
Make the ads relevant. The best part of contextual advertising is that the ads are relevant to your site (AdBrite does not have this feature, they just put up generic network ads). Google and Yahoo both target their ads decently well, but Google Adsense definitely has the best ads that are relevant to your site. To increase ad relativity, make sure the keywords that you want ads for are repeated throughout. For example, if you wanted to display ads related to “making money” you would repeat the phrase making money many times on my page. If you want to be making money, and making money is what you want, then make sure that you are making money by implementing these ads well. It’s also best to spread your keywords throughout the page instead of concentrated in one area like above.
Keep to one theme. This kind of ties in with making your ads relevant, but make sure your website concentrates one one certain type of category. For example, GameSpot.com is a site that focuses on games, while IGN.com has sections over games, movies, comics, cars, etc. GameSpot, if they used Google Adsense, would be serving the most relevant ads - gaming ads. While IGN, if they used Google Adsense, would be serving ads about all sorts of things because they have so many sectors. If a gamer goes on IGN and sees an ad about Japanese Movies, they probably won’t be enticed to click. Of course, these statements are just theoretically speaking, the main point is that if your website is focused on one topic, the ads will be better served to your target audience. If you have a website that covers many things, it will be harder to generate ads that interest your users.
If you're working on a page that's "deep" within a website - consider selectively removing some of the distractions so that more people look at the adverts.
Do your research. Each publisher allows you to create separate channels for your ads so you can track how each individual ad unit is doing. Look over your ads and see which ones are performing the best, and then make a judgement as to which ads you should keep and which ones you should alter or get rid of. Constantly looking over your statistics is a key factor to increasing your ad revenue.