Hello,
First message on this board (although I have been reading it a lot, some contributions have been very useful to me) - early intermediate here.
I think that Hanon exercises should focus on mastering the sound you produce when hitting the keys, and on nothing else. Practicing two exercises at the same time too early may distract you from that goal.
The challenge with Hanon is to make those boring patterns sound as clear and as musical as possible. Before attempting to practice two exercises at the same time, I would therefore practice:
- Changing the "focus note" (i.e. loud-sounding note) in the pattern. Obviously the initial "focus" should be on the first and fifth notes. Having this mastered already makes Hanon much more pleasant to hear.
- Playing stacatto.
- Playing pp.
- Playing p.
- Playing f.
- Playing ff.
- Combining and interverting the above in a single series.
Only after I obtain the perfect touch in each of the above at a good speed (which is not the case right now) will I consider:
- Moving away from C major.
- Practicing the exercises in thirds/sixths/etc.
- Practicing two exercises at the same time.
- Practicing two scales at the same time.
What has worked well for me is to directly start with the metronome set on 108 (the recommended speed in the book), and to play notes in groups : 4+1, 8+1, 16+1, octave, and then full series on several octaves. By fragmenting the series this way, you will identify clearly the points of improvements for the group of notes you just played. Sometimes it will take time before being able to play perfectly and with relaxed hands even the 16+1 pattern.
(When I started Hanon, I used to do full series at a tempo of 80, then 90, then 100, 110, etc. This was a mistake, since it did not allow me to correct the weaknesses in my playing. My mistakes were only played faster. Fragmenting the series at speed is the way to go.)
Only when you have a full series mastered (with musicality) can you then (1) add the first set of variations and (2) start increasing the speed: 115, 120, 125, etc. The goal is always to make the patterns sound as interesting and precise as possible, while staying in rhythm. Someone who can make Hanon sound musical can pretty much make anything sound musical.
These are my teacher's recommendations, and they have worked fairly well with me. Also, as you note, one should not practice Hanon too much - maybe not more than 10mn in a 60mn practice session.
At my level (early intermediate), if I want to practice "brain coordination" (hands doing two different things at the same time) while keeping an emphasis on accuracy and lightness of touch, Bach inventions are the way to go.
Once again, this is just a point of view.