dbacon

I have a rule of thumb for my daily practice. 60% of my time is spent re-inforcing things I can do well. 40% is spent working on stuff I don't do so well. I make sure to keep up all the skills I'm good at, and hit hard things I have trouble doing after I'm confident the other skills are solid. Another way to think of it is to sound great for 60% (of course always sound the best possible) and then push the envelope the other 40%.

I try to end with good sounding material as well, so the horn goes away when the confidence is high!

trumpetpimp

That's a great way to build confidence and make sure you can still do that things you already learned but I think spending 60% on stuff you can already do is a lot. I forget what masterclass it was but the guy was saying that you should sound terrible in the practice room because you should really be spending the vast majority of your time playing stuff you can't do yet. There's no way to get better if you're just practicing stuff you can already do. It makes you feel good but doesn't really make you a better trumpet player.

However, an excellent piece of advice I got from a band director was that an amateur will practice something until they get it right and a professional will practice something until they can't get it wrong. I think this is more along the lines of what you were suggesting.

Of course, this is all just person pracice philosophy and we all know what we need to do do become better and that may not be what your buddy needs to do.