Analysing the musical piece:
The foremost step in practicing musical pieces to play on a piano is to analyse the piece. It is recommended that one should listen to that specific piece in full length for at least five to six times before trying to play it on the piano. If you do not know what you are going to play then you cannot replicate the feel of that piece. Listen the piece carefully, and make sure that you have not missed even a single note while listening in order to understand the piece completely.
Warming up your fingers:
In order to get started, one should warm up his/her fingers. For instance, if the musical piece that you are going to play is in A minor then you should warm up your fingers by continuously playing the A minor in order to perfectly understand the feel of that particular scale and to get the momentum of your fingers.
Practice musical pieces in bits:
If you are practicing to play a musical piece on the piano, it is recommended that you split up the piece into several portions, and then try practicing one portion at a single time. Once you have mastered that portion, and then move on to the next one. Continue practicing until you have done all the portions. Once you have finished all the parts, try to play the whole piece in one go, and continue practicing until you start playing it flawlessly.
Without patience, one cannot learn anything. Learning anything takes time, and it is no different with Piano. Always remain patient, and try to keep your cool if you are not managing to play the piece perfectly.