OWO simply means oral without, when someone performs oral sex on a penis without a condom. This is sometimes the preferred method of oral sex, as many report the feeling doesn't feel as good when using condoms. The lack of a condom during oral sex means that the receiver can enjoy every sensation without a barrier in the way, and many couples practice this as their preferred method of oral.
One of the most essential things to remember when your partner is going to give you OWO is to make sure you are clean... and by clean, we don't mean a quick jump in the shower! You wouldn't be very happy going to perform oral on your partner and discovering they could have cleaned up more, so make sure you do for them what you'd like them to do for you.
Make sure you give your manhood some special attention and thoroughly clean him. Warm water and plenty of soap will help do the trick. If you have not been circumcised, ensure you roll the foreskin back so you can clean every inch properly. Clean the entire area, not just the shaft, to make your partner willing to come back for more. This will help make sure your partner doesn't have any surprises while they're down there, and they can focus totally on pleasing you.
OWO is sometimes coupled with CIM (cum in mouth), however some people do not enjoy the taste of cum and prefer their partner to cum elsewhere. Talk with your partner before and see what they would like best. If they don't want you to cum in their mouth, it isn't the end of the world. They might want you to cum on their tits or on their face, which is great for you, as your partner will be on their knees before you, pleasuring you before you blow your load.