I think that to have a clear approach to promotion is vital for the success of any affiliate marketer. Whilst there is no hard and fast way to complete the whole process, I will outline my methods that have proven successful for me, and many other affiliate marketers. I would like to preface my response to the above question with the point that at the end of the day, we all have to invest either time, effort and money into our campaigns. However, if you are starting from the point of view as someone who is in affiliate marketing to make extra money, as you may be short right now, that is OK, and you can still succeed. The main difference is that you will need to do more work, in the form of promotion, and the model I recommend and use, is the article writing method, as well as blogging. Combining those two methods with some high quality free sites is the key to your success.
I mentioned money in the introduction paragraph, as a possibility, in the form that you could also use paid advertising via pay per click campaigns. That means that people click on your ads to go to your site or affiliate site, but I am going to steer away from that for this article, as PPC is a specialist area, and one that can be successful for some, but an instant wallet-sucker as well, for the unprepared and unskilled.
I have found, from personal experience that writing informative articles is the key to helping people to learn about your product or service. As an example, if your subject matter is dog training, you might go more deeply into the subject by writing an article on the best ways to train a beagle with barking problems. Notice that I have been very specific in my subject area, and not just suggested training for all dogs. The more deep or niche related your subject matter, the more likely the reader will be interested in exactly what you offer. You may not get as many views on your article, but on the other hand, everyone reading your article will probably be interested in seeing the site you talk about in your biography box.
It is important to also give a few points that are useful, and informative in the article. Do not write a sales letter. An article is a piece of information on a subject. It is important that the reader can get something out of the article, and be further informed. If you can do that, you have achieve your goal, in a big way.
The second method of promotion, is to use a dedicated blog, and post to it regularly. Your posts can be in the form of articles, short updates regarding a particular, related topic, or even, full featured articles, and comprehensive data. The format is up to you, as long as you are posting regular content, that is regularly updated. That way, your blog will be fresh, and interesting to your reader, not to mention the search engines, looking for your blog, when it is searched for with the right keywords.