I've done this topic before, but Sonnet Writers has a nice article up that explains iambic pentameter graphically, putting the emphasized syllables in bold. Some of it is a little borderline to me, obviously coming from the "sonnet writer" camp and not the Shakespeare camp, like where he says "Sonnet 30 follows iambic pentameter very nicely." Oh? In which sonnet does he not do that, exactly? And "there appear to be some exceptions" to the 5 (he says 10) iambs per line rule, although there are "logical reasons for these." Maybe he just said that wrong -- they *appear* to be exceptions, but they're not, and here's why.
Other than that, though, he breaks it right down to the individual syllable, explaining when some words run into others ("many a", 3 syllables, becomes more like "man ya", 2 syllables) or the other way around, where "be-moan-ed" is 3 syllables but "van-ish'd" is 2.