The answer to your question is simple: start advertising.
There are a bajillion places to advertise on the Internet, and none of them are better than another. If you want to advertise a software tool for developers, Stack Overflow is probably a good fit. If you want to advertise smiley icons that install spyware on user's computer, then you may want to consider MySpace.
Once you identify a few places that are probably a good fit and might work, then shoot your shotgun at them. There's simply no other way of knowing which audience will be right for your product until you try it. The secret is to spend as little as it takes to find effective data.
Once you find the short list of effective sites, then throw more money at them until they stop working. If nothing works (and your list of sites has other advertisers), then the problem is not them, but you. Maybe its the message, or maybe its the banners.
Whatever route you go, consider the following:
- Almost all advertising is passively consumed; the only reason people pay attention is because the Most Prominent Thing catches their periphery and entices them to spend a second to glance over
- People will visually follow the MPT to the second MPT, then to the third, etc; but, they won’t go to the Second or Third if they weren’t impressed by the first
- If the First and Second MPT are not nearby, then confusion breaks out and some people will go the First and others to the Second
- All of this occurs unconsciously within a fractions of a second
Keeping these in mind, you can avoid a lot of mistakes such as having your company logo be big and prominent.