Choose a subject that you're passionate about. The most important thing to know about blogging is that you have to blog about something you care about. The subject should be something that intrigues you, motivates you, or interests you. You will be researching, reading, and writing about this topic in depth and, if you don't care about the subject area, it will be difficult to keep writing. The subject can vague, like "health", or specific, like "diabetes." Don't choose such a narrow topic that you can't write extensively on it, like "Diabetes doctors in Small Town, North Dakota."
Choose a platform on which to host your blog. The most popular free sites include blogger.com and wordpress.org. If you would like to have your own independent domain name (e.g. http://yourdomainname.com as opposed to http://yourdomainname.blogger.com), this will cost money from the beginning of the project.
Set up your blog. Once you've choose a platform, such as blogger.com, you will need a name for your blog, a template, and a tagline. The name and tagline should be descriptive so that someone coming to your blog for the first time will know what your blog is about.
Read other established bloggers in your topic area. To figure out what you should write about, it helps to see what others are also writing about. Moreover, by become a regular reader of bloggers in your topic area so that you can stay aware of new or interesting ideas and have a community (see step 9). Browse through blog directories like Technorati.com to find similar bloggers.
Write 10 blog posts before posting any content. To ensure that you've chosen a topic that you are comfortable blogging about and to create a first solid set of content, it helps to have prewritten 10 posts before fully launching your new blog.
Sign up for ad and affiliate networks that will earn you money. Google Adsense and Amazon.com are very common ways to make money. Commission Junction and Linkshare are also good affiliate networks that give you a share of revenue if you promote and sell certain products.
Publish content on a regular basis. Start publishing your content on a regular schedule such as daily, 5-days per week, or once a week. The more content you produce, the higher the chance that you will make money.
Spread the word. Email your friends and family to let them know about your new blog. These people will become some of your biggest fans and regular readers.
Become part of the blogging community by linking to others and commenting on other blogs. In order to increase traffic to your new blog, you should link to other bloggers' posts from within your own posts, comment on other bloggers' sites, and request to be put on other bloggers' blogrolls. (A blogroll is a list of other bloggers that you like.) It also helps to submit your posts to "blog carnivals," as these will bring in links and additional readers to your site.
Continue to write and wait. It generally takes a few weeks to start drawing regular readers and ad revenue. After a few weeks, you can try putting your ads on different places on your website to see if they bring more clicks.