In browsing the Android Marketplace I can see countless developers that just don't get what it takes to market their application. Marketing takes work, and a good application is nothing if people aren't using it. Here are five simple tips...
1) If it's a pay app then make sure you release a demo that lets people really try your software out. This means that not only do you need to release a demo, but also that you need to think about how you're going to let a prospect taste your software without giving so much away that they don't buy it if they like it.
2) Include screenshots in the marketplace... the more, the better. I want to see what your app looks like BEFORE I spend my time download and trying it. Besides, if you've put the effort in to make it look nice why not show that off?
3) Use the Android Marketplace. I know they want a cut of the profits and it would be cheaper just to put your demo there and sell your app on your own website, but buying through the marketplace instills confidence and provides convenience to the buyer. You'll make up for it in sales by being where everyone else is.
4) Update your app. Computer software is never truly done... it's evolving with new features, bug fixes ...etc. And every time you upload an update you become the 'head of the class' in terms of the "what's new" area.
5) Get good keywords in your descriptions. As I said in my review, I can't believe Speed Forge 3D doesn't show up for 'racing' and 'line drawing' didn't find Flying Aces. Poor keyword choices... and it doesn't have to be that way.
And as for the Marketplace itself...
It needs more and better categories. And a way to buy gift cards.