There are several main types of patterns used when digging for resources.
Complete Strip Mining[]
Complete Strip Mining
This pattern basically means that you drag out one big dig order over a whole level to clear it completely. To be successful with this pattern you need enough military power to protect the diggers when they often releases several enemies at once. You will also need to keep your storage capacity high or you will quickly waste a lot of resources.
Probing Shafts and Tunnels[]
Probing Tunnels
Probing shafts is a pattern that mean you dig all the way down in several places and after that see where you have more resources to gather. Probing tunnels is the same but horizontally over a level.
One Shaft Mining[]
One Shaft Mine
The one shaft mine is built around a single central shaft from which you expand in all direction but keeping the one shaft as the only way up to the base. That make for easy defence as you can focus traps and guard posts around the shaft.