Study the score to get a full sense of the music. Most hand bell music is written much like a piano part with all of the parts represented in a chordal notation (stacked notes) on a grand staff. This means that you can see all of your fellow player's parts and how they'll interact with the notes that you play. Try to imagine what the whole piece will sound like as you look at the music. If you have some time on your own with the score and can play some of it on piano, this is extra useful.
Work out which notes for which you are responsible. After you've received your bell assignment from your conductor, look to see which pitches and octaves are marked on your bells. The octave numbers refer to which octave the pitch would be on the piano; as a point of reference, middle C is “C4” with higher-pitched octaves having larger numbers and lower octaves having lower numbers.
Mark your notes in the music. Look through the score to find every occurrence of a pitch that is played by your bells. The best way to avoid missing any is to follow each line or space on the staff with your finger and go all the way through the music to find every note. Mark each note in a way that you won't be able to avoid seeing; use a large circle or box around the note head in pencil, or photocopy the music so that you can mark the notes with colored highlighter.
Figure out when you need to exchange the bells in your hands. If you are responsible for more than two bells, you will need to move them around at times during the piece, setting one down in order to pick up another. Make notes in your music about when these switches will need to occur.