I have been practicing like this: I select new pieces that interests me and then, little by little, I first practise the most challenging parts of those new works. I usually have circa 7 to ten new works under this kind of training. Usually it takes a few months to learn the difficult parts of a new piece, of course depending on the piece. After having learnt the hardest part/parts, it is nice to move on and learn the whole piece. Even if I never finished the work, it has still been very good practise for technical skils.

I have been training like this my whole career (30 years), and I have no reason to change this method. Is this a common method? If you want to try something new, why not try this kind of piano practise?

hmm, i dont know if its common or not. i usually just start at the beginning when learning a new piece. but ya maybe ill try your method sometime.