When I gave my friend a blowjob, he climaxed in my mouth. I swallowed the sperm, but didn’t like the taste of it. How can I make sure that it won’t happen again?

Many girls don’t want to swallow sperm. Simply tell your friend. If you don’t, chances are you won’t enjoy fellatio anymore. Ask him to give you a signal before he comes. Guys reach a ‘point of no return’ just before their orgasm, and they know when they’ve reached it. When he gives the signal, you switch to finger and hand work. Another possibility is to use a condom.