If you visualize what you see, feel, etc, then write it. I often actually write things with my eyes closed then come back and see if they match. That being said, don't overdo it! EVER!
If you are getting overly descriptive it becomes a distraction. IE: If you end up with things like "I had my left hand under her while my right arm.." who cares? Just say you had your arm wrapped around them. After all, you might imagine them laying one way, the reader another. That's a huge one that people blunder into.
Also, when setting up your characters you can be deliberately vague with hints and if you keep it realistic your audience will envision their perfect people. That being said, the average 14 year old doesn't have an hourglass figure with DD's, and I have yet to meet a white male under the age of 18 with an 8"+ member, again, unless you are going for exaggeration for some remote reason, let the audience imagination kick it up a few notches. It's easier to portray him as large when she actually feels she has to stretch to accommodate him, and just the same she can be tight enough it takes him a bit to get in or her breasts can be 'a good bit more than a handful' rather than trying to get into the details of it all.
Your mileage may vary of course.
As others have said, have some semblance of a plot, at least a little build-up, and some direction you want to take it to. Without those you have words on a screen more than a story.