First of all, download the Google Play 3.5.16 APK file.
Make sure that you are having file manager installed on your device. This is required to browse from your SD card.
Go to Settings > Applications and from there enable the “Unknown sources”. If you are using Ice Cream Sandwich, Android 4.0 then you will get the same option in Settings > Security.
Now go to the file manager app and go to the location where you have saved the apk file in Step 2.
Look for that download file and tap on that. When you do that then it will start with the installation process.
It will hardly take a minute to install and after that you can use it.