I'd mostly ignore the numbers. The only one that gets reported publicly is the total. On the other hand if you're only generating revenue from adverts then you need a high number of active installs. It would be worth monitoring feedback, competition and crashes.
It also depends on the type of App. I've got some Apps which pertain to annual events and some which are every two years.. You're only going to see interest around these dates. Another is mostly active from March until November.. The numbers ebb and flow with the seasons and so on.
In my experience you need to be updating the App and making it feel current and for Users to feel that issues are being investigated and acted upon in a speedy and communicative manner.
I've also placed my free Apps on Slideme.org and Amazon.
I think you have to ask yourself why people are uninstalling the App, is it because it's no good, or there's an alternative or they've installed on a device for which it hasn't been properly developed (mostly screen scaling issues) and so on. Hopefully you should be getting some feedback about this.
I think most of my Apps have a 4 and a bit star rating, so that's a fairly good measure. Ideally you need to push it, so that it reaches 1k and 5k downloads as soon as possible. Have you got some friends who can install the App and give you some feedback about it? I try to get colleagues and friends to download the App, but give them as little information about it, as possible - to try and ensure that the App is being found. If they can't find it, or don't seem to understand how to use it, then it needs some rework and the description and title need some work on it, to ensure it can be found using keywords or phrases that Users would expect to find it under for instance.
I think some of my Apps have been out for around 3 years now, so have enough years worth of data to understand the seasonal ebbs and flows.
Make sure it's in the Share your creations part of the website here and also mention it on Twitter and Facebook for instance and other forums or forums on which the subject matter is applicable for instance.