maybe try blocking the arms as simple tubes with a ball at the shoulder and elbow before any lineart. the hanging arm reads thin because it stays the same width the whole way. a little swell near the top and a taper at the wrist would help it feel like it holds weight
Sketch / Anatomy trying to draw better anime boy arms
Artist's notes:
I’m trying to sketch an anime boy character and the arms always look too thin or weirdly bent. I think my anatomy and proportions are off. I’m using photoshop / digital, what should i focus on when practicing?