If i'm studying a TAB with just the melody line, i'll just fill in the empty time slot in the measure with the strum of the chord for that measure. For instance, if a piece is in 4/4 time, a beat in the measure may be occupied by a note in the melody. (a note from the lead part), and there isn't anything happening in the rest of the measure. Fill in the empty beats (time slot) with appropriate strums of the chord the piece requires. It helps to have a met when practicing this. I set mine for a slow 1/4 note tempo, (for me a 1/4 note tempo is easier, each note gets 1 beat, for the strum pattern) maybe around 50 or so BPM, in the proper time signature of the tune, most of ours are 4/4. The tune might be melody/strum/, strum/strum/melody, melody/strum/melody, etc, and play it with the click of the met, slowly speeding up as you learn the tune, until you play at the correct speed for the tune. Slow and accurate is always better than fast and sloppy!