I have seen somewhere that folds are actually X, Y, Z shaped. It changed a lot when I noticed it myself. Seeing how other artists simplify folds is also helpful. I observe people a lot, I will just sit somewhere and observe how clothes behave
If you are getting frustrated you can either push it harder or take a break and do something else. Just don't over do it. Studying all the time is tiring and not healthy. Remember to draw something just for fun and you can always apply gained knowledge to your personal stuff.