When you talk about an ex-girlfriend, you give off cues in a couple of important areas:
As usual, we'll get into some of the underlying theory before addressing some Dos and Don'ts. I think it's important to know why something works - that's what will help you grow on your own.
Giving cues as to what kind of women you date is fairly obvious when talking about an ex-girlfriend. Whether you mention that your ex-girlfriend was a ballet dancer, or a PhD student, or a waitress at the local sports bar, the people who you are talking to will assume that such an identity is your "type." They will assume that there is something attractive to you about this specific identity, and they will likely assume that what is attractive to you is the most obvious characteristic about this identity. For example, if your ex-girlfriend was studying for her PhD, people will assume that you like very academic, intellectual, and driven women. If your ex-girlfriend was a shooter girl at a hot nightclub, people will assume you like attractive party girls.
Talking about ex-girlfriends is a very easy way to demonstrate that you are pre-selected to women. Pre-selection is one if the eight universally attractive qualities to women identified in Magic Bullets. Pre-selection implies that other women are interested in you or have been interested in you in the past. Women often use other women's behavior as a cue when selecting a mate. If other desirable women appear to be interested in a man, many women will become more curious about what he has going for him. If no other women, or only obviously undesirable women, appear to be interested in someone, that person may have a more difficult time attracting female attention. This is not only because some women are competitive when it comes to men and dating, but also because women know that most other women are interested in the same general qualities as they are. These qualities, in fact, are the foundation for the eight attractive characteristics in Magic Bullets (mentioned above).
Of course, "desirable" is a relative term. A professional woman in her mid-30s may not feel you are pre-selected if you mention your 18-year old shooter girl ex-girlfriend. A model may not feel you are pre-selected because your ex-girlfriend was a concert pianist. As a general rule, when trying to establish pre-selection by talking about an ex-girlfriend, the woman you're talking to should have the potential to feel a little bit jealous of her, but not so jealous as to be overly intimidated.
People won't tend to ask many questions about your ex-girlfriends. So make sure any information that you want to communicate is conveyed at the same time as you introduce your ex-girlfriend into the conversation.
For example, if you are dropping a reference to an ex-girlfriend into a story about going camping, you might be tempted to say something like "my ex, Cathy, was such a city girl and had never been to the country in her life, which was funny because..." However, if you do so, no one is likely to ask why Cathy had never been to the country and you've lost your opportunity for pre-selection.
Instead, try saying something like: "my ex, Cathy, was such a city girl - she was a ballet dancer since she was like 5 years old and all of her free time was in lessons or performances... no fault to her, it's what made her so successful and it was awesome to see her perform at all of these amazing theatres around the world, but still, she'd never been in a tent in her life. So, it was funny when..." If your ex really was an internationally-known ballet dancer, this would be the way to communicate it.
This is tricky. When you're in a larger social situation, it is unlikely that people will ask you too many follow-up questions about you and your ex-girlfriends. On dates, this happens more frequently. Often, a woman might ask you why your last relationship ended, or, if you bring up an ex-girlfriend, why you broke up.
This is a great opportunity to be positive, but also convey what it is you are looking for in a woman. This should be something attainable for her, but only if she is at her best. It can also get into...
You can have a lot of fun with this. Imagine a woman is asking you why you and your ex-girlfriend broke up. You can start by saying some nice things about her and how you are still very good friends, but that you two were just fundamentally different.
For example: You were more of a passionate, spontaneous person. Like, one weekend you told her to pack her passport and her overnight bag and wouldn't tell her where you were going. To surprise her, you took her to Paris (or Montreal, or Las Vegas, or whatever) to your favorite restaurant - just on the spur of the moment. You're more that kind of person, and she's more of a planner - she was happy and sweet about the whole thing, but you could tell the whole time that she would have rather had her guide books and maps and lists of things to do picked out and weeks to prepare. Or sometimes you'd bring her flowers or a stuffed animal, just for the hell of it. She'd always wonder what it was that you did wrong... she just didn't get the spontaneity. That was just one of the ways you were too different. She's dating a lawyer right now - he's a great guy too - and they're going to do really well together.
In all, it's an opportunity to communicate positive characteristics about your relationship behavior that you would not be as likely to be able to say directly.