If you are talking about regular pop rivets, I drill the head out with an oversized bit (for a 3/16" rivet, I use something like a 3/8" or 5/16" bit. Once the head comes off, punch the rivet inward with a punch slightly smaller than the rivet hole.
If the shank of the rivet is still in the hole it can throw the bit off center and make it impossible to cleanly drill it out. In that case, you will need to grind the head of the rivet off with a dremel or side angle grinder before punching it out.