Advertising is easy to start, making it a popular income stream for many bloggers. However, it’s not nearly as lucrative as it once was and it requires a lot of traffic to be truly profitable. Also, it runs the risk of frustrating your readers (ever been on a site only to be assaulted by the ads?) and making your site look cheap and unsophisticated. Therefore, it’s not a top recommendation of mine.
If you want to be famous or reach a wide audience, you will have to choose something slightly broader and work hard to make the best content for that topic. A subtopic relating to fitness, finance, or relationship advice is likely to reach the most people. Consider specific but broadly applicable topics such as managing money in college, or a marriage counseling blog.
Lets say, for example, that you refurbish and resell used smartphones out of your home. You could use a blog to attract visitors to your website where you list your current phones for sale. Your blog might cover topics about DIY refurbishing. On one level, it seems counterintuitive because you want people to buy your phones, but it also helps you build a brand and gain recognition. Social media guru Jay Baer explains the concept on Copyblogger:
I will quibble on one point though, your comment about BBT getting 13,000 subscribers before launching even though you “had nothing but a coming soon page and an invitation to join our email list.” As I recall, you also had a freakin’ awesome video on that page as well that just made people yearn to give you their email address, even without knowing a thing about BBT. So that didn’t hurt, either. ; )
Consider a free blogging service. Many people opt to create a free blog using popular services such as WordPress.com or Google Blogger. This is a good option for people who aren't familiar with web design, don't want to pay for their own hosting, or enjoy the ease and stability that comes with these services. These services do have limitations on how you can make money using them, however, so make sure your blog won't break the terms of service.
The time you invest to make any significant amount of money is the same amount of time it takes to build a course or other offerings. If you want to make good money with ads (in the thousands), then you need to get 100s of thousands or millions of pageviews a month. This takes time and in that time you could just as easily build up your mailing list, create an infoproduct and make thousands whenever you want.
Affiliate sales comprise a large chunk of revenue for most big-name bloggers. For instance, Pat Flynn made $53K last month from affiliate sales, compared to "just" $9,500 from book sales. In general, look for affiliate products with higher price points; web hosting companies are a great choice if it makes sense in your niche, with payouts of anywhere from $60-$130+ per signup.
I know many personal finance writers with blogs that track the financial mess they got themselves into. They don't have financial degrees, but they are doing very well for themselves and help many people with their experiences. Many times, readers just want to hear from you, follow a real person's journey, read about how a real person made it through a problem, and so on. This is a great example of why degrees are not always needed.