How to not use data up on Iphone 4?

I had a limit of 2gig of internet when I got my phone activated through Verizon and now the internet won't work and I went back to the store and the manager said it was because I used up the limit of data on it. How do you not use the limit of data on it?

Use Wi-Fi whenever possible. Disable Push Notifications, don't Google something unnecessarily, and straight out don't stream any videos without Wi-Fi. YouTube is the kiss of death. 2 GB is pretty high, so abide by these basic rules and you should be fine.