Choose a key before copying the original
The original key may not fit your range. Use Piano to check whether the lowest and highest notes are comfortable before deciding whether to transpose.
Turn hard spots into drills
The hard part is rarely the whole song. It is often one high note, long phrase, turn, or ending. Fix one at a time.
You do not need the whole lyric to practice well
The useful question is where you get stuck: which note, which phrase, or which breath. Marking those spots helps more than rereading the whole lyric.