1. Get Vajra
2. Create Flat, Meteor, Charged, Scorched Surface Mystcraft age with as many Dense ores as you want (I usually go with 20 or so)
3. Dig down to your desired depth and run in a straight line holding down left click (Vajra digs so fast that all the decay won't be able to catch up to you and even if it does Vajra one shots it
)
4. ????????
5. Profit.
This works best if you have a sorting system setup with an Ender Chest so you can just dump you inventory into a pouch. Your inventory will fill up with various ores and dusts VERY fast. Some people would say that this makes the game too easy so use at your own risk. I personally don't think it makes it too easy because I still run out of copper all the time and have to go mining regularly for that and also I barely get any uranium so I've only got 3 Hybrid solar panels so far even thought I've gotten at least 3000+ diamonds. This method does make Iridium rather easy to get tho, after a whole run using up my entire Gravichest I usually have 20+ Iridium. Also if you added the Mass Fabricator recipe back you can macerate all those diamonds and use it in the mass fab instead of scrap and this will give you quite a bit of uu-matter (I believe 2 diamond dusts = 1 UU)
If you can't afford a Vajra just yet make an age with 1 or 2 dense ores and Meteor, Charged, Scorched Surface. The bad effects should balance out with the dense ores and you should have little to no decay. Then just mine as you usually would and you should get quite a few resources that way.