If you are actually taking about the icon/logo for the app, you'll probably want to spend some time working on it. It's the first thing that a user sees, and so can have a surprisingly significant effect on engagement. You'll also want it to be unique enough to stand out amongst other apps, but not so ugly as to encourage the user to delete it.

I'm definitely not a designer, so I use a professional designer for real (consumer) projects. For just an app icon, creative talent is actually pretty cheap - e.g. fiverr had 225 listings for 'app icon.'

While it is a bit intimidating to roll your own, it isn't actually all that hard. Here's what I've done:

1) Download a few component SVGs from http://thenounproject.com . For example, if you want a star on your icon, search for 'star' and download the one you want.

2) Load all of these SVGs into Pixelmator, or an Adobe tool, or GIMP.

3) Resize/recolor/shade/layer the individual SVGs until you get something passable. Save it in a very high-resolution as a master.

4) Resize this master into all of the different sizes you need. I think Android has roughly five different icon sizes, from 144x144 to 36x36. If you're comfortable on the command line, ImageMagick does quick work of this resizing.

Good Luck!