The current state of the online advertising market is often the topic of articles or news stories, and while the market isn't as good as it was a few years ago, its not completely without promise either.
Back in 1999 it was not uncommon to find ads for $20 CPM or more, even untargeted ones. There was a lot of venture capital flowing into poorly managed Internet businesses and these businesses spent a lot of that money on advertising. The subsequent failure of these businesses has had many decrying online advertising as worthless, this is not true. The real reason these businesses failed is because they had a poor business model, not because online advertising does not work. In fact there have been numerous studies showing that online advertising does work, people just expect too much from it.
The Internet is unique in that you can very accurately measure how many people take immediate action upon seeing your advertising, so advertisers place unrealistic expectations on their advertising campaigns and they don't realize that there are two results of an advertising campaign. The first is obvious enough, immediate clicks, however the second result, increased brand awareness, if often ignored. Most TV advertising is for branding purposes, very little of it is designed to yield immediate actions such as an impulse buy for the latest product from Igia. However advertisers have yet to fully grasp that while you can track click-throughs online, it doesn't mean branding is worthless.
In fact some advertisers are even taking advantage of this. How many click-throughs a banner gets is highly dependent on banner design, so there are advertisers who design a banner to get low click-throughs on purpose. They then sign up under a CPC pricing model and get a multitude of branding for relatively low cost. The opposite is also true, the most clickable banners out there are never sold on a CPC basis but rather a CPM one. Both of these practices are bad for the publisher but good for the advertiser. In order for this to change CPM prices need to go up so that people who design clickable banners find CPC advertising the better choice.
Typical ad rates these days vary. You can still get $10 or even $20 CPM for a targeted advertisement, but untargeted ads can bring in as little as $0.5 CPM or worse. Typical CPC rates vary from 10 cents to 50 cents, but most CPC campaigns bring in relatively little effective CPM unless they are targeted to your site. As prices have fallen to these lows the quality of ad has also fallen. It is very typical to find abrasive, annoying, and deceptive ads being used. In their most benign form they resemble a windows message box that most people are smart enough to realize is a just a banner. In their most malignant form they will prompt a user to download scumware or in one case programs were installed without the user even knowing.
The typical website, especially when starting out, will be a member of an ad network. There are many ad networks out there, some popup seemingly overnight, and close just as quickly. It is important you research any ad network before joining, there has been many cases where an ad network goes belly up before paying it's members. There are also networks that pay late or otherwise are undesirable. For reviews on advertising networks check out our advertising category.
Advertising networks all have various requirements for joining. They all usually have a traffic requirement for a certain number of monthly uniques or impressions. They also often have quality requirements and topic requirements. Even though some networks have traffic requirements under 10,000 impressions a month, I recommend you do not serve any advertising until you reach atleast 30,000 impressions a month, and depending on your site maybe even 100,000. The reason is that until you reach that point you won't make much money anyways, and you'd be better off spending your time building traffic.
Another issue you should be aware of is that you don't need to join just one network. Most join multiple networks and then feed defaults from their first choice, to the second choice, and from their second choice, to their third choice. This allows you to cut down on the number of defaults you serve.