You really need a good visual designer to help make a great looking app, in my opinion. Beauty is in the eye of the beholder, of course, but you can make good looking apps with judicious spacing between items, making sure objects are large enough so as not to look too tightly packed, and coming up with a color theme that has just a few colors in it, and sticking to that theme through out the app - including in icons. Fairly large (48dip at least, but x2 is okay) squarish buttons, flat, with icons, a flat 2D look and a color theme go a long way.
You should check out a couple of the YouTube channels Google has:
The App Clinic: http://www.youtube.com/playlist?list=PLB7B9B23D864A55C3 This is a neat show where two techs review applications in the Google Play store and discuss the UI, design, functionality, and gives tips on improvement.