The first friend I made after starting public school when I was young turned out to be bi. He's only interested in settling down with a woman--which I why I consider him straight. To that effect, he once slept with a mutual friend (girl) and she told me about it. Let's just say he doesn't last as long with girls...

Consequently, I'm further inclined to consider him straight.
At any rate, we used to do all sorts of stuff together: spar, explore / hike, play video games, &c.. In the summers I'd spend a lot of time with him, and frequently stay the night. I was out to him but not really comfortable with my sexuality. He used to dig on me for it a bit, too, which didn't really help. But we were generally comfortable discussing sex. One night we were talking about it, discussing our naive opinions on the differences in dynamics between straight and gay sex. Late in the night (early in the morning), he admitted he'd played with his ass some but could never find what he thought might be his G-spot. He also confided that one of his biggest fantasies was getting fucked and jerked at the same time. It was surprising to me, but ultimately I felt it didn't really matter.
We talked about fooling around when we got a little older, just because we thought it was perfunctory. At any rate, that night he said he was hard from the conversation. I was a little horned up, but a little tentative to do anything. I wasn't sure how I felt, and his parents were in the next room! (To this day I think his mom heard us.) Still, I told him the only difference between college-aged and now was time. He said he was game if I was, so we messed around in his bed that night. For a while we were obsessed with it, just trying different things and always making plans to steal away to the woods or hang out when the house was empty. We did it only periodically after that summer.
It was fun. We don't really do screw around any more. Our lives have taken different paths, and work eats up most all of our free time. We're both "slight" workaholics, with positions a little beyond our age in my opinion. We still visit every now and again and our relationship is very amicable.
Apart from him, I don't really have any experience with straight guys.
My only advice would be to test the water. Drop hints, but don't do anything so outrageous that it plucks him from his comfort zone. It also usually pays to get to the point. A lot of times, the other party, if interested, is feeling the same ambiguity (mixed signals) and experiencing the same uncertainty and trepidation. Sometimes it liberates them when you dispel the mist and put the cards on the table, so to speak. It also seems to help to incorporate a "failsafe," such as either party can call quits any time for any reason, no questions asked. Of course honor it. If you pry or whine or nag after he's called quits, you're disrespectful and dishonest, and that will torpedo whatever bond was being built. Same goes for him.