. . . to say “thank you for advice”, according to one Sensei I met, is to actually implement the advice.
After correcting a student’s technique, explaining to them what they’re doing wrong and how they can do it properly, it’s always interesting to see them doing the same thing wrong during the next repetition of the drill.
Sometimes that’s inevitable. I don’t expect students to fix ki-ken-tai issues after one mention. But for some things that are easily corrected (maai, for example), it’s always a treat to have to repeat the advice. Repeatedly. (Hmm. Where’s that sarcasm font when you need it…?)
So, don’t just say “thank you” when a Sensei tells you ways to improve. Try it. Maybe it’ll actually work. Then keep doing it.