Start by buying Joe Friel's, Cyclist's Training Bible. You'll read this book and read it again, and again, and again to absorb the advice that he dishes out. I've been racing off/on for almost 20 years and still refer to this text for advice.
There is step-by-step advice for crafting a training program based on the number of hours you have available to train. BTW you should focus on hours not, miles, becuase you may do lot's of climbing which takes lots of hours but not lots of miles. To be competitive I would say that you'll be looking at a minimum of 300-350+ hours per year. Most Cat 2-4 racers I know are putting in between 400-800 hours per year.
The other thing I would recommend you do is find a local group ride and learn how to handle yourself in a pack. You'll need to learn to draft and move around in the group, ride in an echelon/paceline, and ride a straight, predictable line.
Last, be patient. If you're just starting out, and you don't have a solid aerobic base or lot's of raw power you will be pack fodder for a while. I was dropped countless times in my first year of racing, and it was humiliating and infuriating (I sound like Jackie Chiles). So enjoy the journey! You will get better!