hammer on...

i built my HD from a kit serveral years ago but never could really get the hang of playing it. i was playing a little mando, chord back ground stuff but now that i'm older i couldn't play the mando anymore due to arthritis, so i'm trying to give the HD another wack. The thing i'd like to do is play in the background, similar to how you play chords on a guitar or mando while somebody else is playing lead or singing. how would you go about doing such a thing? i've seen plenty of times where the HD just takes over everything in a jam and everyone centers on the HD, finally nobody else is playing and the HD is strictly playing the melody and the jam dissolves. any ideas on how to get started are greatly appreciated...