• as in bingo, your chances of success may go up if you play two or more cards
• but only to a point!
• simpler melodies often allow for more rhythmic and harmonic possibilities
• a song you know well enough to sing from memory allows you to rely on your ear more
• avoid notation at this stage
• learn to play the song by ear from memory (listen to recordings if necessary)
• understand the relationship of the first note to the key
• play the song in other keys
• use the paper keyboard to internalize the melody further
• consult written music only to check your work
• if you wish to sing along with your arrangement, choose a key that is comfortable for you
• otherwise, choose a key that centers the melody in the octave just above middle C
• pro tip: jazz musicians often prefer the keys of F, Bb, or Eb

Other resources:

• Piano keyboard ear training aid