Actually, Alexa ranking is not based on your real traffic as your rank is determined by the number of visits from people who have Alexa toolbar installed in their browser. Try Entrecard and be more active in webmaster forums like DP. Good luck. You might be interested to visit my post on Alexa Traffic Rank. How To Improve Your Alexa Traffic Rank How I Broke Alexa Top 100K in Less Than 3 Months Improve Alexa Traffic Rank Good luck.
You should not rely on Alexa's rankings at all. They are so open to manipulation, that its not even funny. Their results are not safe at all.
hahaha i got waz-warez.org 400k /month only 54k alexa rank but my site only 50k/month got 44k alexa rank i really dont understand why alexa do this....
Alexa ranks based on their toolbar so even if your site might have huge amount of traffic (say in thousands every day) it might rank low compared to a site which focuses on "webmastering" or "SEO" and has much less traffic (say in hundreds every day) cause most webmasters have alexa bar installed and those hundreds are using that bar. Hence places like DP, Sitepoint, Entrecard, Adbrite, blogcatalog, etc ranks high... The fact that your ranking went down could be because the people who used to visit your blog have uninstalled the alexa bar, or new people are visiting your site and those old people arent (those who had the alexa bar installed), so though you might have the same traffic in general but alexa traffic decreased. Or, other sites are doing simply better than yours. Hope it helped you.