Well it depends on what you want to do with it...

You can either have him, cum on you, or on him, and clean it up with Kleenex, a wet towlet...etc.

Bascially you clean up and throw it out. Just make sure that he lets you know when he's about to climax. That way he can aim to the appropriate location. - Be it, a tissue for the garbadge or your mouth to swallow.

Another option, is a condom, if you choose when youre giving head to use one, that will catch the ejaculate and its just a matter of tie up/throw out.

Keep in mind, where he cum's, make sure you're careful that it doesnt get into/around your vagina. (lets some residu on your/his hands, for example) - Seriously that is how people get pregant without actual intercouse - it really shouldnt be a problem, just dont be naive, is all.