Ah - you don't. 180 followers is like saying "How do I run a successfull restaurant with 1 customer per day."
You will have to wait until you have a real number of followers - possibly about 100 times larger than what you have now.
Until then, the usual google adwords (showing ads) is about your only approach, but it also will not exactly be making money. Simply not enouh volume here for anyone to care.
William, I love tumblr but it is mostly a non-commercial social service (unlike Facebook which is an ad network masequerading as a social service). I use it for personal scrapblogging, and the majority of blogs on tubmlr are not monetized because they are also used for personal reasons. As a community, Tumblr feels a bit like a modern LiveJournal. It's just not the right place to try to go big with any kind of spam blog or affiliate blog or whatever you might be considering. The Tumblr TOS allows some ads/links but commercial use cannot be the main purpose of your tumblog. I have only one tumblr with ads in the margins, so it is possible to do so by customizing your theme (ad zones and text links) but the platform lacks any tools for tracking your traffic and conversions and is just an all-around poor choice for a typical monetized blog (that is, monetized with ad buys or affiliate offers).
And as NetTecture mentioned, 180 followers is no big deal. A follower or fan is not even as valuable as a unique visitor because who knows how often they even pay attention or click-thru to your content? I have many blogs with over 10k uniques a month, and I do monetize these blogs because they are self-hosted on Joomla and/or Wordpress so I have unlimited tools to manage ads and links. If you would like to create a blog to monetize I strongly suggest picking another CMS/framework like Joomla!, Wordpress, or Drupal (the learning curve on Wordpress is probably the smallest if you just want a plain vanilla blog).
Don't be discouraged, but do be realistic so that you don't invest a lot of time and hope trying to monetize a tumblog with that level of traffic. Even my very best affiliate programs do not convert better than about 1:350 clicks (and most visitors do not click your ads, so trust me that it takes some time to build an audience of targeted traffic and find ads that work). Much more common are 1:1200 ratios or worse for low quality traffic. Also optimizing and testing affiliate links and ads is a very time-consuming job. If you don't know anything about monetizing blogs, the good news is there are thousands of tutorials freely available online.
Hope that helps, and do consider Wordpress for your blog if you want to monetize someday. :)
It all depends on what niche your blog is in. Make sure the ads are relevant to your content.
Here is the biggest thing: Make any ads you put on your blog not disruptive to the readers. Don't throw them right in the middle of your post text (on new posts, you can on old posts, see below). Like if your blog is about domain names, put up some small 150x150 ads in your sidebar linking to places like GoDaddy.
Another way to monetize is look at your analytics, and find all the posts that get a lot of search engine traffic. Add some Adsense to those posts only.
Getting sponsors or writing sponsored posts on your blog can be a great way to monetize your Tumblr blog. Social Spark and Pay Per Post both provide opportunities to earn money by writing blog posts about topics that interest you and your readers. Additionally, you may want to check out Fiverr. There, you can post your own jobs and let the orders come to you.