well, i've never had sex with a best friend. so i'm not exactly speaking from experience.
but if i may throw in my two cents, can i ask what you are asking from this experience? do you want to have a relationship with him that goes beyond being his friend? if this isn't what he wants, then you might end up very disappointed. (btw, the vice versa is true on his end).
can you openly talk about birth control options with him? can you ask, "hey, i think i like these condoms, but what about you? ribbed? or contoured for extra pleasure?" this applies to dating couples, too.
have you read the sex readiness checklist? you might think you're ready, but are you **really** sure. and it won't hurt to read the article, it's not like you'll be blinded thereafter.
are you afraid of feeling gross? are you afraid of being naked? are you afraid of retribution by higher beings? then sex is probably not the thing for you right now.
personally, i'm not a big fan of sexual experimentation just for kicks and curiosity. some people are, and that's just fine. but i put a lot of emotional stake into my relationships (i'm neurotic!), and i simply can't handle playing or getting played because i feel like i've been let down, or i feel like i've let myself down.
anyway, good luck. do what you think is right
The Second Law of Thermodynamics states that the universe is constantly moving to a state of greater entropy s, therefore, delta s is always greater than zero.