I would be now publishing my first app on Google play store. I have already compressed images used in my app. And I have some questions regarding the app size.
If you are using a PSD to get the images for the app, those images might not be optimized for web and devices. You Photoshops "Save for Web and Devices" to optimize the images. You can reduce lot of kbs from this.
Next, see if you can replace images with XML drawables. For example, buttons and background can be done using XML