When I have female children, or rather when my future daughters grow up into teenagers, I will not become an overprotective father that shields his precious daughters from the dirty boys.
I will teach my daughters about their sexuality. I will tell them to explore it, but to do so carefully, and don't do anything unless they're sure they want to.
I will make sure they are taught everything they need to know about contraceptives. I will make sure that they have contraceptives available in case they need them. And I will not tell them categorically that they shouldn't have sex. I will however tell them, as mentioned, that they shouldn't have sex unless they really want to, that if they have sex they should make sure the boy uses condoms. I will not show disappointment if I learn my daughters have had sex with their boyfriend, but I will make sure they know I will be disappointed if they do so without the use of contraceptives. Not angry, just disappointed.
I will tell them never to be afraid to tell me about anything they've done. I will not, and I'll make sure they know that I will not, harass any boyfriends if I find out that they've done something with said boyfriend they shouldn't have done, as long as the boyfriend in question did not coerce my daughter into doing it. I will especially not do anything like that if my daughter told me about this herself.
If any of my daughters do something stupid and later regret it, I will not get angry at them and condemn their actions. I may be disappointed, especially if I believe they should have known better, but I will be supportive and understanding.
I will ally myself with their cool aunt, or their 10 years older cousin, or someone else like that, and have that person teach them a bit more about intimate details that it would probably be way too awkward (for both parties) to discuss between us. I just hope my kids will have such a sexually liberated older family member that they could comfortably talk about such things with. I'm thankful I had an aunt like that.
When I have daughters, I will let them do their own mistakes, but I'll make sure that they do those mistakes with all the information I wish I had had when I was a teenager, and more. And I'll make sure they know that they can always come and talk to me about their problems.
Okay, realistically, I will probably delegate a few of the things above to the girls mother. And, obviously, the validity of some of the statements above are affected by the age of my daughters. The freedoms above would be gradually earned as the child aged. But by the time they are, say, 15, I will strive to keep true to all the statements above.
Also, please note that the above only goes for the specific topic of sex and sexuality. I may let my daughters do what they want with their boyfriends (within the bounds of sanity and safety, of course), but that doesn't mean I'll let them go out and drink, party and be generally irresponsible. They'll have limits.
For the record, all of the above also goes for any future sons I'll get.