I'll weigh in with my typical advice:
1. It's not your raw MPG that you should worry about, it's your relative MPG. If your typical commute and driving style give you 40 MPG in the HCH, then you would probably be getting only 30-32 in a regular Civic.
Your relative MPG will always be a constant 20-35% better than in the equivalent non-hybrid.
2. Your driving style can definitely make a difference; but an overwhelming factor is your typical commute or trip; if it is favorable, you can easily meet or beat EPA numbers. If not, then you won't.
E.g., if I commuted into the city, about 25 miles per day, I would easily get 50-55 MPG just by going 60-65 MPH
. But I don't: my commute is six miles, down/up hill, with 13 stop signs and traffic lights. In the winter, my car is barely figuring out how to autostop by the time I pull into work. I squeak out low-to-mid forties in MPG.
So your typical drive is going to have a major difference on your MPG. However, the good news is that you can relax, because your relative MPG compared to an equivalent non-hybrid Civic is still going to be 20-35%, no matter how good or bad your typical drive is. So as the our Aussie friends say: no worries!