Usually even heavier users are fine unless you do streaming audio or video which will eat it up pretty quickly.

If you add any wifi networks you may have access to that helps a lot. Also if you adjust the fetch/data sync settings that can also help you be more data efficient. Many aps for social networking or e-mail frequently connect and check for e-mails/status updates etc. How frequently they check is a user adjustable setting.

Verizon should print how much data you've been using with them on you bill or on your online account manager. Assuming you're using a smartphone with them you should be able to get a pretty good idea of what you've historically been using.