Translate the song using the lyrics sheet into signs using your sign language dictionary. Because song lyrics may not perfectly translate with sign language, attempt to translate phrases as well as possible. You should end up with a literal translation of the song.
Determine the pacing of the signs according to the syllables as they are spoken in the song. Generally you will have one motion per syllable. Keep in mind that many signs have several motions, possibly more motions than there are syllables in the word it represents, and you will have to slur the sign together, condensing it into fewer motions. The exception is when you have to sign letters, in which case you will have to spell out the letters within the time of the word being sung.
Create some simple dance steps that will use your body language to communicate the emotion of the sign.
Memorize the lyrics to the song along with the signs. You will need to sing along with the song at the same time as your are signing with it.