Finally a topic of interest. Though, I'd strongly suggest you to delete what you wrote about exercises. Not that I agree or disagree very strongly, but it will make the topic go and be about exercises,and not practicing.Now, to the topic. In general, I start with the thought "I won't stop with this part until I can bring it to lesson, without looking stupid". It means sort of, if I know how I can improve it, I don't continue until I no longer knows.
I start with trying to sight-read the piece (badly). Then I usually start at the beginning. Except if I am not secure about being able to learn I might start with the hardest looking part. I usually work on one phrase at the time. But I also take smaller sections (like one measure) if necessary to "teach my fingers". I often first try to play hands together, get an idea of the correct rhythm and how the hands connect. Hands separately if I need to work on the fingering. I alternate between slow and fast practice (my slow isn't always slow enough, but it's very difficult for me to play slow because my concentration fails). While doing it the piece becomes somewhat memorized, but it's not really secure. Only after I am able to get through the piece somehow, I can really start concentrating on details.After I managed to get through the whole piece like this, I try to get the whole thing together. It's just play (either in sections or the whole piece), evaluate, practice what wasn't good enough, play again, evaluate, practice...Still changing and correcting things, sometimes even fingerings. I still go back to hands separate and slow practice, until I feel it's as good as it can get. If I have trouble with remembering things, I add more "starting points", which means I practice starting from different spots than what I used in going through the piece. This I could go on doing forever, but at some point new pieces take over...Oh, and in this stage I also record and listen...and often decide that something needs to be changed or notice little mistakes...
Now, to the topic. In general, I start with the thought "I won't stop with this part until I can bring it to lesson, without looking stupid". It means sort of, if I know how I can improve it, I don't continue until I no longer knows.
Done Now, when I read that, the question arises, HOW can you improve it until you no longer know how? This, of course depends on the type of passage practised, but generally HOW do you go about getting it ready for lesson? You might use slow practice, or you kind of "force" the passage to work by repeating it over and over again? There seems to be some kind of strategies behind your thoughts...elaborate!
But the point of lessons is to teach you what you don't know, and help you with what you can't do. The "stupid looking" thing is exactly what teachers look for because this is where they can really do their job.