Read the documentation from Google itself
The steps should be simple to follow.
Please follow this doc from google for complete publishing details
In short,complete steps in a nutshell(I am assuming you use eclipse/android sdk):
1. Check android_manifest.xml and verify that android:debuggable attribute is set to false in your manifest file
2. Check the android:versionCode and android:versionName attributes.
(if this is the first time you are uploading a apk,
ignore, else if it is a new version of existing apk, make sure these
values are larger than previous apk)
3. Export unsigned application package from Eclipse
4. Sign the application using release key certificate(not debug key certificate)
5. Zip align the package
6. Upload in google play