I'm still doing quite easy pieces in piano. I've moved up from Grade 3 to Grade 4. Last year I was doing Grade 7. However, I'm finding it very challenging. I'm to play the pieces I'm working on with the metronome - exactly with the metronome, and with the correct dynamics. We discussed why louder is always faster (you strike the keys faster to make them louder), which means that you have to have more space between the notes if you're playing louder.
I'm back to working on technical stuff too. I had to stop for a long time because of trouble with my arms, but I seem to have that licked for now. One of the things I'm supposed to work on this week is to take any major scale and play it with the metronome set at mm 100, one quarter note per beat for one octave. OK, that's really easy. Now, without a break, play two octaves of the same scale with two eighth notes per beat. That's fiendishly hard. I'm still struggling with that. I'm also back to working on triads, arpeggios and dominant 7th chords - all with a metronome. Also chord sequences I, IV, I, V7, I - of any of the scales I'm working on.
I like working on the technical stuff - it's very calming; you just get in the groove and go. Unfortunately, I can't seem to find "the groove" for the scale work with the metronome, but am working on that too. I do find that I have to do only a little bit at a time - 10-15 min. max, or my arms start objecting. That's also ok.