Adding a advertisement is the main way that you can make money from your blog.
Some people make more than millions of dollars from there blogs using advertisements and it is a best and the most legit way to work at home or earn money online.(see the top 10 blogs in categories)
Now How can you put your 3rd party advertisement in your blog?
This a HTML code of a Banner Medium Rectangle (300x250)
<!-- Begin BidVertiser code -->This code is looks like this, If you click this banner or a text link i can earn from them, if you are a USA citizen i can get $1 to $5 from a one click.
<noscript><a href="http://www.bidvertiser.com/bdv/BidVertiser/bdv_xml_feed.dbm">xml search</a></noscript>
<!-- End BidVertiser code -->