The After-Sex glow is the feeling of euphoria one gets after really good sex. It might last just minutes, or a whole day. It might be described as a bit like the pleasant parts of being drunk, without the dizziness. Or, it might be described as similar to the feeling of being on an adrenaline rush, only much better. People in this state often have red cheeks and a silly smile on their face and are unusually giddy and happy. From what i can tell, these are the best ways of increasing the chance of this effect:

have sex with someone you really love a lot. This is the best thing ever, i definitely recommend it.

have sex with someone you are very physically attracted to (hopefully also the person above). This is also an extremely good thing

have sex in the morning, so the effect can last longer and can be coupled with the overall newness of morningtime.

make sure your partner has a good orgasm too, its a reflective thing and much better if two people experience it.

as far as i can tell, masturbation never results in this feeling, even after doing extensive research on the subject. Also, i have no idea if casual sex can have this result, since i've never had casual sex. If anyone else can enlighten me, feel free to node it.