Like the title of my blog andriod market is simply a War Zone
When you are building your first android application you need to understand that it's very tough out there.
We started couple of months after the announcement of Adroid Market ,with few cool applications mainly related to EMAIL & SMS.
The feedback was great and we earned ~1k USD per month without any promotion just because the application was useful.
Nowadays it's another story, you'll put the coolest app in the world and you'll get a lot of bad feedback & zero visibly in the market ,so you'll need to put some extra effort on publishing a free version put YouTube and maybe also push via advertisements(e.g. Admob..).
It'll be very hard in the first couple on months but with a useful application eventually the users will notice it.