Select a song appropriate to the level of your music-reading and piano-playing abilities. Simple arrangements may include nothing more than the melody of the song or the melody accompanied by a simple bass (left hand) line. Piano pieces typically come in simple, intermediate and advanced arrangements.
Get a recording of the piece you want to play, if possible. Hearing the piece can accelerate learning how to play it. Read along with the sheet music as you listen to the recording. This is an effective way to learn phrasing and hear how the melody and rhythm work together.
Determine the key and time signature of the piano piece. These are located at the beginning of the sheet music. A series of sharps and flats tell you what key you'll be playing in and the time signature (written as 4/4, 3/4, etc.). These two pieces of information can give you an idea of what to expect with chords and scales used in the piece, and the timing structure.
Break the piece into clefs and play through each clef to become familiar with the notes you encounter. Play the treble clef (the top staff in the sheet music) first, then play the notes in the bass clef (the lower staff). When you are comfortable with the notes on both clefs, play them together, combining your left and right hands.
Set the tempo on your metronome to a slow tempo, such as 60 beats per minute. Your sheet music will have a metronome tempo marking to tell you the speed at which the piece should be played correctly, but start at your own pace and work on learning the piece before you try playing it at the appropriate tempo. This will help you iron out any rough passages before you try them at the right speed.
Play the piece at the appropriate tempo until you have memorized it and can play it without looking at the sheet music. This may require playing the piece many times. Or if you have a good memory, you may memorize the piece quickly.