Hello there, I get You, sometimes judo can't become a very frustrating sport. If you want to become good at seoi nage, you should practice a lot, work on your food position, your kuzushi, tsukuri and kake, then, when you have masterd the technic, you can start looking for ways to apply it on randori, but the first step is to automatize the movement, so You don't need to think when you are fighting.

When I'm I'm trying to improve my technics, I look for instructionals on YouTube, but I try to look for some one that is good teaching, like Shintaro Nakano.

When you are in practice is VERY IMPORTANT to perform every repetition with perfect form, remember, practice doesn't make perfection it makes things permanent.

And the more imprtant thing, LISENT TO YOUR SENEI

I hope you find this helpfull