A useful trick is to understand which notes two chords have in common - for example, C major (C E G) and G major (G B D) have G in common, so by holding down both bars (don't think it works on electronic ones, though) you will only have the G strings playing.

I use the technique to get a waltz time 'dum ching ching' effect, where 'cum' is two bars held down (in this example C and G) for the bass note, and 'ching ching' is one bar for the chord (G)...

With a bit of research you can even do bass runs, and it can help to make a melody stand out more clearly.