A very good Alexa Traffic Rank for smaller websites would be 50 K but that's pretty hard to achieve.
Personally I've never bothered with working on my Alexa Traffic rank because it doesn't matter that much and Alexa Traffic Rank stats are not that accurate anyway.
I just focus on getting more search traffic through Yahoo, Google, Bing and other search engines and focus on writing more stellar content that is highly searched to bring in the search traffic needed to earn money with my website.