try emphasizing curves on the figure. your lines are really angular, try making them flowy. think of a down comforter vs. a tire. you want cushy softness. her jawline is also masculine, try bringing it in to the right a bit more.the thing that struck me most was the size of her feet. big feet are definitely a defining male feature. lastly, giving her alot of eyelashes or emphasizing the breasts almost always works. very stereotypical, I know, but in art you do have to cater to stereotypes to get your point across. I hope this helps. I know I had the hardest time getting my men to look masculine, and still do. don't give up though, just think stereotypes and soft squishy things.