So, the practice object is what we set out to absorb.
What that object is will be defined by musical phrase, spatial movement, fingering sequence, tonal balance or any of those in combination. It could be anything that requires special attention, for whatever reason.
In depth study will lead us to conclude that everything deserves correct absorption, for no part of a musical whole is less deserving of our attention than another. Quite often the parts we regard as the "simple bits" are found to be lacking in sincerity and authority if they are overlooked by our attention and may even be found missing from the memory when it comes to performance trials!
Notice the omission of the word "difficult" which is purely a relative judgement and has no place in the mind of a Pianist, upon the black and white way.
Seeing practice objects, (all be they self set goals) as purely matters of science, sets a positive attitude in motion.
A practice object is simply the current challenge you have set yourself.
Thoughtful consideration of the context of this object, combined with the scientific methods at your disposal, plus determination and applied concentration will yield the desired result.
It must be born in mind, however, that concentration is a somewhat limited resource which tends to become less effective the larger the area it is applied to.
Concentration is like marmalade.
Imagine a teaspoonful of marmalade spread over a slice of toast the size of a football pitch and then imagine the same amount spread over a piece of postage stamp sized toast.
Now think of the effectiveness of the marmalade in both cases.
The idea, therefore, is not to choose too large an area as your practice object. Be very disciplined and try to resist the temptation to attempt to play a piece in its entirety (badly) simply for the reward of reaching the end.
That time will come.
Enjoy the learning process. Relish seeing yourself becoming the best teacher in the world, be patient, scientific, artistic with yourself.
Start off with small sections for the beam of your concentration to tackle and gradually work those small sections into larger sections taking care to make the joins inaudible. Try to work between firm "posts" in the music to help you integrate the rhythm, always bearing in mind the context - what comes before and afterwards - so that the small section reflects as much as possible the realistic conditions of its eventual performance. Energy flow, rhythmic law, degree of relaxation are all useful observations at this stage.
Avoid, wherever possible, practicing at an irregular tempo, or you will find it makes no sense if you try to apply rhythmic law (covered later on.) It matters not to play slower than the eventual pace so long as the pace is consistent with itself. Pace will come with your mastery of the practice object and it is simply a case of “scaling up” what you have already achieved until a suitable pace becomes manageable.