My mines have always been very simple. Dig down to the appropriate depth for the ore. Dig along until I’ve used a stack of torches then branch off either side at 4 block intervals (3 blocks between each branch). With 1.18 coming out I decided to up my game a little and create a proper mine entrance and a decent sized shaft (ooh er missus).
To that end I spent a little longer than usual on the surface preparing the mine entrance and included a camp so that it has that rustic frontier mining town feel to it. Rather than muck about with houses or huts I went for a tent which quickly became a more workable tarpaulin. I will probably change out that gaudy yellow wool for light grey wool at some point. I also used some logs to give the feel of support at the entrance and fence posts on the main stairs and shaft (which is now 3 x 3) in the same way that the generated abandoned mineshafts do. And then I decided to splash out on using lanterns for lighting which gives it a much more rustic mining feel and left any ores exposed on the main shaft.
When I’d finished mining out a branch I used to close it off with a block of cobblestone with a torch on it so that I knew if had been mined. Again I’m changing this in 1.18 for wooden fences. Since most of the mining is in DeepSlate for diamonds, I’ve used spruce fences at this depth (higher up I would go for the more traditional oak.
Mining diamonds in 1.18 is painful (at least in the first few days). Firstly diamonds are prevalent at Y -58 however to make any progress you need iron pick axes and iron is most prevalent high in the mountains. So there has been a LOT of running up and down. Secondly mining DeepSlate (even with a diamond pick axe) is slow. Really slow. It takes twice as long (0.6 seconds) to mine DeepSlate with a diamond pickaxe as it does to mine stone (0.3 seconds) so basically your search for diamonds will take twice as long. That said I have only completed two of my branches so far so I may still yet hit the mother lode. Just out of interest I put together this comparison table for some of the mineable blocks (where a diamond pick axe is the tool of choice) from quickest to slowest.