Newer iOS has bn known to save data so updating might help. You might also want to avoid:
1. Anything that streams. YouTube is a data hog, try to avoid it.
2. Online gaming. All those graphics are costing you data!
3. Maps, they continuously download a lot of temporary data.
4. App Store. Even though apps are capped at 50MB for cellular data, a 50MB download translates to about $5 on Econet data bundles... So try to use iTunes on your PC to download apps and updating apps.
5. Push notification. For email set push to manual rather than scheduled intervals. Switch off push on apps that u don't really use.
Also you can instal onavo (search it in the AppStore) it will help conserve data and track which apps are taking the larger chunks of your bundles