@fluffy @hideki that's hard to say. I don't think design courses work, at least not in the sense that they teach you to design stuff you want immediately. The best bet would be practice - you sketch several concepts, look at them the next day, draw again, a little bit better, look at improved concepts the next day, until the result is good enough. Repeat for several months (or years), and you'll gradually get better at design, or drawing, or modeling, or whatever you want.
For me personally, a good exercise to get better at drawing was drawing insects from photos.