To go along with yesterday’s post, here’s another thing to consider. Much like technique is never really perfect, it just develops, a difficult section of a piece grows over time.
You cannot fix everything in one day. It’s about shaping your playing of a section, slowly, and deliberately avoiding mistakes, into what the end result is. Using practice techniques like stop go practice or separating the hands is one option.
Let’s take the Villa Lobos Etude no. 1, for example. The arpeggio pattern is not easy, and it’s especially not easy to sustain it through the whole piece at tempo. So you could isolate the right hand. And work on simply doing the pattern once at tempo, completely relaxed. Then work up to twice. Maybe doing some thunk practicing (muting all the strings with the LH while the right plays) to listen for perfect rhythm, or slow/fast alternation, or altering the rhythms to develop more control and evenness, or crescendo then diminuendo the pattern. The goal is to make the pattern feel effortless for extended periods of time.
Now that’s a lot of stuff just for the right hand, and we haven’t even talked about the left hand! The goal is to slowly get our hands used to playing difficult sections, shaping technique from the start so it feel effortless later. I am always working on the VL #1 right hand pattern. To start I worked in speed bursts until I could play the entire pattern once at tempo. I suck at a m a alternation, so I ended up practicing a lot of p i p i p m i a m (plant a) just working up to the a m a part. I have trouble getting a back to the string, so I practiced doing that until it felt easy then continued. It was not a short time that I spend doing that. Weeks, actually. I still practice that at least a few times each day, especially now that I’ve returned to the etude.
Practicing a difficult part is about breaking it down, practicing it perfect from the start, and slowly shaping your muscle memory to give the desired results.