My mines tend to not show on the maps; I start mine shafts under my base and branch them out from there.
Layout/style has evolved over time, but I tend to build a 3x4 staircase going down to bedrock, throwing down a landing every 6 - 8 blocks down, where I'll do a 3x3 hallway on either side of the landing that is about 25-30 blocks deep.I then do a 3-1-3 branch on either side of each tunnel. Seems to work for me.