I find 4 note chords a bit muddy usually, and use them sparingly. I play most of my chords on the left hand, so that's what I'll refer to here. I try to use as many different ways as I can to play any chord to add a bit of variety to the sound. Before I decide how to play a chord, I write down all the notes in the chord - say C7 = C,E,G, Bb, then find where those notes are on my instrument.
I then look at all the different ways I can play some or all of those notes, and decide what combinations I think sound best at each point in the song / tune where a C7th chord is needed..
I usually omit either the 3rd or the 5th, so in C that would be C, G, Bb, or C, E, Bb.
Sometimes I only play 2 notes, that's any one of the C chord notes (C, E, or G) plus the Bb 7th note - it all depends what sound I want or what I'm playing before / after the 7th chord, and what anybody else might be playing.
Sometimes I play the Bb above the C, sometimes I play the one immediately below it, - with an accordian reeded instrument this can sound ok as there are lots of harmonics which stop the two notes clashing and sounding ugly.
Sometimes I only play the 7th (Bb) note sustained on its own, as a change from 3 note chords played before / after - to make the accompaniment more interesting or as part of a bass run.
Sometimes I ignore the fact that it's a 7th because I can't find a way to play a 7th that sounds good to me.
Just some ideas - there are no rights or wrongs - it's your instrument, your music, if you enjoy the sound you make and it fits with anybody else you're playing with, then it's fine.
Good luck, have fun!