While these top 5 topics to avoid may be relevant, I would advise any man to avoid the subject of your personal perceptions of sex, including what you find attractive or unattractive in other women to be Number One on my list.
Women do not need to know how it feels to you, in particular, to sample every chocolate in the box. Details to a woman get analyzed to the Nth degree, exaggerating the tiniest details until they begin to have nightmares.
Discussions about previous relationships are not taboo. However, you must remember that--in general--people are not perfect. No one wants to be remembered for their faults and shortcomings. If you discuss another's faults, your girlfriend will rightfully wonder if you are doing the same thing, telling others about intimate details that she considers to be private.
It is perfectly natural for your girlfriend to ask about the type of qualities you admired in previous girlfriends, as in intangibles, such as kindness, compassion, empathy and so forth. It's the skeletons in the closet you need to avoid discussing--at least until she knows you well. Then, be cautious about the subject matter; so that whatever story you decide to share will not "freak her out."
In addition, women tend to ramble when talking on the phone; so that their smallest flaws are aired without her taking the time to think about how her gushing may sound to you. Do not obsess over the small stuff. Privately, she may feel fat in her stomach,but do not make the mistake of calling it a "third boob" or make any other inappropriate remark. I can guarantee she will never forget it.
Lastly, put yourself in her place and think how you would feel to be put under the microscope. Your finances are your business. However, if you are in a serious relationship, finances are the responsibility of BOTH people.
Once you reach the serious stage, you will have learned from your mistakes. If you do not learn, you will not have a girlfriend for very long.