Look on your local calendar and see if you can find anything that is labled a training race or that might have a class before hand or mentors that ride along. We have both around here. Tuesdays there is a circuit race series that has beginner and cat 4 categories for women and has ride along mentorship. Thursdays there is a crit series that has a beginner/cat 5 field (unfortunately no separate womens field, but women and juniors get half off the entry fee...) that has a class before the race that is free with your entry.
She Fly is totally right there really is no way to tell if you are ready than to jump in and try it since there is no experience quite like the pack, but I would strongly encourage basic group riding skills to any one first. At very least you should know how to safely draft and paceline and you should know how to corner safely. You should be comfortable riding in your drops, epsecially through corners and down hills. Don't get discouraged or insulted if someone says something to you. It can be tense and since no one wants to fall they can get vocal. Just try to listen objectively - you may be doing something without realizing it.