First, teach by example. Talk about the challenges you face and the decisions you make with your children (after the fact). Explore their thoughts on the subject, asking them what they would do in that situation. A parent's job is to prepare her kids for adulthood. If we explore as many possible situations with our kids as we can, when they face those situations, they will have a tool belt of options to choose from. It sometimes isn't what people want to hear, but one of the most important aspects of parenthood is spending time in meaningful conversation with your kids, which means giving up something else you might like to do.
As far as sexuality is concerned, the topic will inevitably come up in conversation, and all a parent needs to do is answer the child's question honestly and appropriately without showing that you are nervous. I also agree with DeathKnight's statement about the stage of development. Research stages of development, and make sure you are not asking a child to understand something that is beyond them. For instance, 5 year holds do not understand abstract terms like "how would you feel if you were in their shoes?" So the concept should be explained in concrete terms.
That said, you can't control your children, you can only guide them, and hope that they retain the morals you have taught them. Children are more likely to retain a parent's morals if that parent has a trusting relationship with the child and if the morals are instilled from a young age using rules, rituals, and traditions. If you find that a bit manipulative, which I admit it is, then you should find out what is important to your child, and develop a tradition based on that.
For the record, I am not a parent. I recognize that this is easier said than done. I do work with kids, however, and take parenting classes weekly. Actually the parenting classes I take are free to the public, offered by the local community college, so if you are interested, you might be able to find something like that in your area.