For me, it helps reading tutorials on how to do it first. There are some great ones in sims4studio website x x x. 

Once I got those down I watched video tutorials and people doing speed videos.For the poses to look natural I usually look for images to use as reference or I try doing the pose myself to see if it’s even anatomically possible. Hands and fingers are always tricky. Looking at your own hand gestures definitely helps a lot here.

Other than that, it’s just practice. The more you do the better you’ll do. Good luck!! :3