The way to write effective sex is not to write it any differently than anything else. I mean, I've been saying for years that I write sex the same way I write fight scenes and I write fight scenes the same way I write conversations.
And that's exactly it.
A sex scene is not different from any other character interaction. You present it in exactly as much detail as is useful and/or revelatory. And as for the readers who fetishize it one way or another (who won't read sex scenes, or who focuses on the sex scenes....) well, I say screw 'em. I don't make special allowances for people who skip the fight scenes or the dinner scenes or the trudging across the tundra mile after mile scenes.
If it's in there, it's because I thought it improved the narrative. If it's not, then it's because I didn't.
(Please note, if you're going to apply this principle to writing, it's important to make sure you're not just writing your kinks, because the squid in your mouth is only interesting to people who like to watch trains wreck. Also, this does not apply to writing erotica. I don't know bupkiss about writing erotica; nor do I claim to. This applies to writing plot-and-character-driven genre fiction.)
And if you want to know how I handle sex in narrative, there's at least one example in the sample of By the Mountain Bound that's up over at elizabethbear.