If you've only got a 1 or 2GB plan, adding a data-saving app like Onavo Extend might be a step in the right direction. You may remember my post about Onavo Count, an app for calculating your data usage, which is very similar to this one. The big difference between the two is that Extend takes saving data a step further by using its servers to compress data you request before it gets sent to you.
This app does come with a couple of caveats, though. First, it's not ideal for large file downloads, as it will reduce your speed. Second, some Web sites may not load properly, or at all, but this seems to happen in a limited number of cases -- as noted by comments on the Google Play Store. (In my experience, all of the Web sites loaded.) However, you can disable the app at any time if your download speed is too slow or you find a Web site that won't load.
After those two steps, that's it. Now you can continue using your mobile device as you normally would. If you need to disable the app, just open it and tap the button. Don't forget to re-enable the app after you're done with your download or Web site that had issues loading.
As an added perk, Onavo Extend can tell you which applications are using wireless services most often and destroying your data caps. The megabytes or gigabytes used by each app will display in a table upon opening the app. so you can figure out which ones are your worst offenders.
What do you think? Give it a try and leave your feedback in the comments.