Like a 'fade to black'?
That's pretty easy actually. You can have the scene leading up to it be hot and heavy with making out and other intimate things. Get that implication down really good and then just have the characters move into a bedroom or give consent to move forward with sexytime and then gently end the scene.
I think it is really important to end the scene specifically on both a high note of happiness between the characters and also gently because at the end of the day it is an entirely intimate moment. It is important to maintain a gentle and loving relationship not only between the characters but between the characters and the reader. You want to make sure that the reader is (somewhat) satisfied by the goings on, even if it is a fade to black.
For example (And forgive my character choices):
Harry shifted and Ginny made a sound of protest as he stood up. Where did he think he was going in the middle of all this? Didn't he see how much she wanted him? Just as she was about to voice her displeasure, Harry extended his hand towards her with a soft smile. "Come on." He whispered, eyes still glimmering with intensity. Ginny took his hand, only to blush a little when she realized where he was leading them. Her bedroom. A soft 'oh' escaped her lips as she stepped inside. Harry shut the door quietly, before reaching for her once more. It was only a moment before they had collapsed onto her bed, picking up where they had left off.
-End Scene-