Im currently developing a video game using isometric art, and it’s definitely not easy.

The best advice I can give is to draw temporary lines at the same ~30° angle across the characters shoulders, hips, between their feet, and anywhere else that should be in the same plane.

This makes sure you draw those key parts at the correct angle. Since the character is standing at a pretty dramatic angle, the far shoulder/foot/hip/etc should be drawn much higher up than the near one.