Certain browsers allow you to disable loading images. The AOSP browser is one. Don?t think Chrome allows it. Disabling java-script should help too.
Don?t auto-update your Google Play apps over data.
Go to Settings and in each of the entries under Accounts, uncheck everything.
If you set up a POP3, IMAP or Exchange email account, then set the sync frequency to manual.
Be wary of people sending you large files over IM apps. E.g., Whatsapp has a setting for ?Media auto-download?. By default, the app will auto download images over data. You?ll want to disable that and check your other IM apps to see if there?s anything similar.
But tbh, rather than limiting your device this way, you should look into getting a good data plan.