Instructions
Examine the bottom layer to understand your goals. The objective of Diamond Mine mode is to use matching gems to break away dirt. When two layers of dirt have been removed, the drills dig down to a deeper level. It is important to understand what gems are touching the dirt layers so that you have an objective.
Maneuver the gems to create gem combinations on the bottom-most level. Matching gems in the upper levels get you points, but but most of the game's points come from digging deeper. Prioritize making matches on the lower levels. If it not possible to achieve any lower level matches, then make upper level matches to change the gem composition. Once you have brought new gems into the field, you might be able to make matches in the lower levels.
Make four-of-a-kind or five-of-a-kind matches whenever possible. These high-value matches create special stones that explode or create other devastating effects.
Match special gemstones wisely. For example, if you have a special gemstone that explodes all gems adjacent to it, then it is wasteful to make it explode in the upper levels. Try to make matches beneath the special stone so that it comes closer to the lower levels, and then match it to make it explode.