You can have adsense...you can also sell links..you can offer reviews.. These all depends on what quality of blog you have...
you can also do affiliate marketing i.e you write a good review about a product and put a link to the product. You can put ads on your blog. Or do get paid to review site, software
To earn more, you'll need more traffic. Traffic = visitors. Your aim right now is to try to get as many daily visitors as you can. It doesn't matter what your money-making source is. You can't make money without your visitors.
adsense is the first and easiest thing... but blogging is just like playing a game... you have to build your character first and so does blogging, you have to build your blog first
I agree with the above about adsense. The other way is to join an affiliate (like Pepperjam in my sig) Out of the list of companies that are registered with Pepperjam, you pick out which ones compliment the content of your blog and post their ads. You'll get paid if a click through makes a purchase.
First try to build up unique content, followed by handful of traffic. Then you can sell banner spots, uploading adsense, signing up with affiliates like CJ, Neverblue ads etc. will do the rest to fill up your wallet...
For all these you need two basic things, 1. Google Page rank 2. Alexa rank Advertisers see only this when choosing their banner spots on your blog.
Honestly it's very hard for small blogs to earn a decent income. Selling ads directly from the marketplace here in DP is what works best for me You need to provide full traffic details, the url and a price to interested buyers.
Let's not forget the Corporate blogs. Their sole purpose is convert readers (or SE traffic) into direct sales or leads for their Company.