As children, boys and girls need the same advice, in my opinion. I think they need to know not only to "not talk to strangers" or "don't get in the car with strangers", etc., but to have some knowledge of what "stranger" actually is, and what "bad strangers" will often say to fool them. My kids know in advance who we will send if something happens and we can't pick them up (my mother or sisters, or my brother-in-law), so they are NEVER to go with someone, even someone they know, who says that my husband and I are hurt or otherwise unable to get them. They also know not to go up to a person's car, and if a grownup asks them for directions, or to help them find their lost puppy or kitty, they are to go get a grownup (any caregiver, including school personnel) to help the person.
My kids know that if anyone touches them in a way that they don't want to be touched, they need to say no. To clarify, they also know that if anyone touches them "where they wear underwear", that area is off-limits and they need to say NO! loudly, and then tell someone. NOTE: My five year old is a bit of a ham, so when he ran out of the apartment a few months back in nothing but his Spider-man Underroos, it didn't seem odd to him that a neighborhood boy with a camera phone took pictures of him, so the "underwear rule" also definately applies if someone wants to see their underwear.
My kids have never been afraid to talk to strangers, and I'm okay with that, since in real life, we have to talk to "strangers" a lot. Allowing them to "talk to strangers" does require a lot of extra attention, though. Basically, my theory is that it's perfectly okay to say "hi" to the girl at the check-out line at Target, but the grown man who occasionally goes up to the playground without children "to read" wierds me out. Basically, I'm pretty much monitering what my kids SAY to strangers, and make sure they understand they aren't to go anywhere with ANY stranger.
With young children, boys and girls are pretty much at the same risk. As they get older, though, the risk for boys tends to lower after puberty, while the girls' risk goes up.
I've read that one in three kids (anyone under 18) have been solicited online by a sexual predator. This is definately the highest risk, so some internet/dating safety is important. Girls, in particular, should be careful, because they most often don't realize how easily they are to trace from something like a myspace page. For example, on myspace, most people put the school they go to on their myspace page. If you have a girl who has her school displayed, and there is any hint that she is part of any club, either sports, cheerleading, drill team, choir, band, theatre, whatever, she's just given any predator with a phone and a brain a way to stalk her. Say the person knows which school she goes to, and that she's in the upcoming production of Oklahoma! All the person needs to do is to call the office of the school anonymously, ask when the production of Oklahoma! will be, and show up. Your fifteen-year-old daughter's online sexual predator could be sitting right behind you watching her sing her little heart out about how "She's just a girl who cain't say no". Not to mention, a lot of teenagers put comments back and forth on their pages, saying when and where they're going to meet someplace. Once again, your beautiful daughter has just advertised where she will be in case anyone wants to stalk her.
Plus, there's just common sense stuff. When your daughter is walking through a parking lot after she gets her license, make sure she has her keys already out of her purse, ready to unlock the door and get in quickly. If it's dark and she's having to walk through a parking lot, let her know that she is to get someone, either an employee, or a security officer, to escort her to her car. Most all stores will be perfectly happy to oblige, because it is a really good safety measure.
And then, of course, there's just the usual safety stuff. Don't have a private date with a guy until you feel 100% comfortable with him. To begin with, have a cell phone and your own transportation, and meet in a populated, well-lit place. Don't leave food or drink with a date, even for a few minutes. If you must leave to go to the restroom, rather than drink the soda you were drinking, ask for a refill. These days, the so-called "date rape drugs" are a very real threat.
As strongly as I do not believe that a woman "is asking for it" by wearing provacative clothing, etc., let your daughters know that there is a stigma out there, and that her risks can increase if she is dressed or behaves in a certain way. My mentioning this does not mean that I think it's okay, but I think it's foolish to possibly put yourself in harm's way over the principle of "I can do anything I want" or "I can wear anything I want".
It is every bit as important to emphasize to boys that age that anyone (male or female) can say STOP at any time, and that at that point, you need to STOP. As funny as the episode of the "launching sequence" on Everybody Loves Raymond was, there is NEVER a point where it's too late to turn back once you've gotten things going. Also, boys should be aware of the fact that girls aren't "asking for it" by wearing certain clothing or doing certain things.
With either sex, tell them there is no shame in asking for help. If anyone violates them, it is not their fault, it is the person who hurts them. Telling someone and getting help is not a sign of weakness, it is a sign of incredible strength.