1. First decide whether you are going to blog for yourself, or for a network. Blogging for yourself and blogging for a network will open up different ways to earn money. How much freedom you will have over your topic, the time that will need to be invested, and structural limitations will all be a factor in how you answer this.
2. Blogging for yourself will have standard ways of earning money. Things like Amazon affiliates, Google Adsense, and Other affiliate programs will all vie to be part of your blog. Amazon affiliates will pay a percentage of the sale for everyone that comes to purchase at their shop from your website or blog. This is great if you do many book reviews or highlight certain products in your blog. Google adsense starts paying out once you reach a $100 threshold, and pays when people click ads or links from your blog. This is good when you have topic that has higher paying keywords. Other affiliates, such as Art.com and other site specific places, will typically pay you a percentage of sales generated from your site. You can register at places like Commission Junction and pick which advertisers that are similar to your topic and have them on your blog.
3. Blogging for yourself can also pay you for things called a PPP. A PPP is a pay-per-post, where advertisers pay you a set fee to include links to them and a short write up (usually positive) about what makes them tick. Some of the companies that do this are Blogsvertise, PayPerPost, and BlogHer Ads. These places typically pay -X- amount for a write up in your own words. Some require the blog to be a certain age or a certain page rank on Google. Check with the companies prior to signing up to see if your blog qualifies. Blogsvertise is good for beginners, while BlogHer typically has a better reputation.
4. Blogging for a network will usually pay you either in ppv (per page view) or a set amount. Blogging for companies like B5media are highly respected, while blogs like About.com come with some serious perks. About.com currently has a minimum payout of $725 a month. In a land of Suite101 and being paid per page view, B5media and About.com can really show that you've made it in blogging. Requirements are varied for network blogging. B5media requires six to eight posts a week. About.com requires two full-length articles every 14 days and update to your blog one to three times per week.