I've already touched briefly on how to identify high paying topics, but there is additional monetization research you can do before embarking on your publishing endeavor.
The first and easiest thing you can do is buy one of the many "Top Paying Adsense Keywords" products out there. There are many companies that are publishing information on top paying contextual advertising keywords, and while their accuracy may not be 100%, the trends they can illustrate are fairly accurate. So do not look at the costs per click associated with the keywords in these reports and use it to calculate your earnings, but rather instead use it to identify keywords or topics that may pay more than others.
You can also do your own keyword research by opening up an advertiser account at Google Adwords or Yahoo Search Marketing. In both cases you'll be able to get an idea exactly how much advertisers are paying for keywords by trying to buy them yourself and seeing how much it costs for each position.
You should also research potential affiliate programs. Believe it or not people often, and successfully, build websites around and specifically for a single affiliate program. If you can locate an attractive affiliate program with a quality product that you can market, good conversions, and good payouts, then consider building a website around the topic of that program, especially if you've located a niche which is underserved at present. There are many ways to build a site around an affiliate program, but the easiest way to do it is usually by making a review site for the business or type of product being sold in the affiliate program. This is a type of resource site as I mentioned in the Website Types article.
Once you have found a topic you like and you think will be profitable, you need to analyze the current marketplace for that topic to decide if there is room for you in it.
The easiest way to analyze a niche is to simply search on your favorite search engine for the keywords most closely associated with your niche then examine the top results returned. Do these sites look professional? Do they have good compelling content or products? If the first site is good, what about 2 or 3? On the Internet you can still be very profitable even if you aren't first place. Once you've gained the SEO skills talked about later in this guide you will also be able to judge the relative degree to which the sites have been optimized, and obviously less optimized sites are more easily overtaken.
In some cases you can even do undercover work and ask the publishers of the other sites for information on their site, they may just give you traffic or income statistics. You can also research domain ownership using WHOIS tools to figure out if the site is owned by a larger company or just a person.A later article in this guide will deal with what is called a Keyword Effectiveness Index as a way to analyze the existing level of competition for a search keyword.
Not every website type is a good fit for every website topic. Blogs are best fits for hobbies or professions, as are forums or ezines. Resource sites are good for product, tool, or business directories. Reference sites are great for topics in which there is a lot of information and topics which more information is definitely better. Forums too do best with popular topics, the more popular the better. So extremely small niches might be better served with a blog or small content site, at least at first
My recommendation is that if your topic does not mesh with your preconceived idea for the type of site you would like to run, then don't force it, reconsider your decisions.
As always if you have any questions on anything in this article or need help implementing the advice provided, come ask the friendly people in our forums.