Here's a little tutorial that's how I measure their body, and the main measurement is face/head and any part of it, like length from hairline to chin, nose and chin, eyes and chin, eyebrows and lips, ears to chin, etc. you can double it and so on.

I thought Tae seemed too petite compared to JK, but then I measured their sizes - they're just as they are! I knew Jk is really buff but I was worried if I didn't make him too buff lol WELL he is BIG.
Here in the photo example the width of Jk's chest in profile is just of the size of his head's length while Tae's chest in profile is smaller.

In drawing human body artists measure the height and any body parts by the length/size of head, for example standard is 7 - middle to 8 heads - very tall. And classically, nipples are positioned on 2nd, navel is on 3rd, and crotch on 4th... (of course every type of human body varies I'm just talking about the classic, also, depending on dynamic of pose, plus perspective, the size\height can shrink or become taller/bigger and each pose specifically changes those classic rules, so you don't have to be precise about millimetres!
Talking about references... I put them chaotically, use them and delete them later (except the pics of boys - they're treasure), so anyone who asked me for references - I'm sorry I don't usually keep them. For one art I can gather about 10 to 20, or even more references including figures, color palettes, backgrounds etc. and after that I usually delete everything because I don't wanna keep stuff I won't use again, it's lips napkins, you wipe, you throw.
Omg Taehyung's legs are aesthetic tho...

Also, I pay attention to details... and I even care about stuff that aren't visible, like this ...

Even when you can't see it, you're gonna feel it lol
Next: coloring is rough, just to see the light and harmony first, I'm not the type who likes to draw things carefully, I like it quick and sketchy - that's how you feel the impression.

For me, defining light and shadow is the first and the ever most important stage after filling the color. It gives you a room to know what you should work on.

So yeah, that's the main process of how I usually work ^^
Hope you like it and find it helpful <3
Miss you guys! ~ X