I would like together with a friend and play songs together. I play both the piano and guitar, and he only plays guitar. I tried it first by recording myself playing a pop song on the piano (only chords just to see how it would sound like) and then I tried to accompany it with guitar (both electric and acoustic). I found that playing the same chords doesn't really always work, so I searched the internet for advice and I found only one source. Thus I ask here for further information.
I imagine that the question is too broad and one might have to specify a genre. Hence, I formulate the 2 questions and you can answer to whichever you think makes more sense (or both).
Can you give some general notes-advice on how to accompany a piano with a guitar (or vice versa)?
Can you give some notes-advice on how to accompany a piano song with a guitar (or vice versa) on specific genres? (I am mostly interested in pop, ballads. You can add for other genres if you are more familiar with them. Other people might find it helpful.)