I can tell you a little bit. No, wait, I can tell you a good-sized chunk about sex. Uggh. I just failed at that joke because I referred to my wang as a 'good-sized chunk'. That's how you describe how much foreign material is in your stool.
Let's start over. Good sex is what happens when I blow a load and no one hits me. That's a better joke.
Good sex, I suppose, can be many things. A lengthy romp in the sac with nowhere else to be and all kinds of fun stuff. But personally, I think good sex is when both people have an orgasm. For some, this is a common occurrence. For others, it is not.
If you can't figure out how to finish yourself or your partner off, there are other places you should go for advice. I recommend 'useyourstupidmouthyoustupididiot.org'.
If you're in the orgasm no problem line, then I guess good sex is when you have a simultaneous orgasm, so that you're both yelling at god, pounding your feet and high-fiving at about the same time. This is achieved in my experience by these factors:
A female partner that comes easily when she senses that you're about to.
That's it. I'm a dude, so making me come is as hard as making me cry at one of those videos of someone being reunited with their dog. It's much more of a challenge to line up the timing of the lady-finish. It can be difficult; not all dudes can hold on until the right moment, and not all of us are lucky enough to have a wife who responds so quickly to their impending shazamining.
Sadly, I'm one of the lucky ones, so I don't have a lot left to say other than this: Who gives a shit? Do lots of stuff and don't be a selfish fucker, and you'll both be happy in the end. (If in the end made you think of in the butt, I like you.)
Short Answer: Put the stiff parts near the wet parts.