There are a number of different ways to earn money from your blog. Below we listed some of them but it is by no means a definitive list. You will most likely be able to find more ways to earn money if you look.
Affiliate links
You can post affiliate links in your blog. If someone buys something through an affiliate link (as an example at Amazon) you get a percentage of the value of the sold product. Affiliate links can be a very good way to earn money on certain types of blogs. They are especially useful if you review products or have an otherwise product related blog,
Contextual Adds such as Adsense
Adsense and other similar add solutions are very practical as they take care of finding and targeting the adds for you. All you have to do is to install the ad code and then you can focus on content and they will provide the adds. Adsense can give high revenue but it is usually possible to get a higher income by posting affiliate and CPA ads. Adsense is usually very good for content/information centered websites and is a good beginner options due to their simplicity.
Intext adds
Intext adds such as kontera changes certain words in your text into adds. If someone clicks the adds you get paid. Inlink adds in themselves seldom give much money but they can be used to earn a little extra on sites that are already featuring other types of ass as well.
Clickbank
Clickbank feature a high number of electronic products that you can sell on your website and earn large commissions. Click bank products are available in very diverse areas and you can likely find a suitable product no matter what your blog is about.
Sell your own products
Creating and selling your own products does not have to be hard. It does take some time but will allow you to earn a lot more money than you will get from selling other peoples products.
Selling Links
(This is against google guidelines) If your blog has a lot of visitors or at least some page rank (3+) than you can sell links in your blog roll or in blog post to other people wanting to promote their websites and blogs. You can either rent link space to people monthly or permanently for a one time fee.
Sponsored blog post
Sponsored blog post are blog post that you are paid to write. You are often asked to include certain links or to review a certain products when doing sponsored blog posts. It is ethically recommendable that you mark sponsored blog post as such so that the readers know that you got paid to write it. If you want to write sponsored blog post you can visit payperpost.com