Install a Eclipse IDE for Java EE Developers 3.5 or 3.6 (3.7 is not supported). You can download it from Eclipse Downloads page.
Download and install the latest version of Flash Builder plugin for Eclipse.
Starting from Flash Builder 4.5 the procedure for acquiring Flash Builder plugin has been changed. Prior to Flash Builder 4.5 there were separate downloads for Flash Builder standalone and Flash Builder Plugin for Eclipse.
Installation of Flash Builder 4.5 as an Eclipse Plugin requires two actions:
See Flash Builder release notes for more detail.
Install the Android SDK and Android Eclipse Plugin as described in Installing Android SDK and Eclipse Plugin