Playing it subconsciously, you will always want to use the color gems that you can deal damage with. But continuously doing that for around 3-5 turns, you will notice that most of the unrelated color gems are starting to build up.
There are two ways of dealing with this:
Skill #3a - Start Low (Level: Basic)
"Start Low" is a skill to remind you that, the more you attack, the more unrelated gems you will stack up at the bottom of your screen, like below:
|Oh I need to attack with green!|
|Oh wait... now what...?|
|There's three more... lets attack!|
|Now what again...|
This is a BAD EXAMPLE. Don't do so unless you are confident or just rushing to finish the dungeon!
So, why not start with the bottom of the screen, and slowly build some combos using the unrelated gem to move them around? That way, not only do those unrelated gems get eliminated off your screen, but also helps you combo up your damage! You are killing two birds with one stone! The following video will show you guys how to start at the bottom rows to make some combos.
Skill #3b - Clean Up the Mess (Level: Intermediate)
"Clean Up the Mess" is another good way of dealing with something like this. It is to use up one turn to eliminate most of the unrelated (or weak damage) color gems. The following is video of me using this skill - while cleaning up the mess, I can still deal decent damage and keeping every turn a chance to attack again!
|See all those green gems there? These are "irrelevant" gems.|
|If you can, eliminate them while do some combos.|
|See all those green (irrelevant) gems again?|
|Clear them up using one turn. Makes your life easier next turn!|
Applying these skills on top of #1 and #2 will definitely refine your combos in harder dungeons.
Was a short one, but hope you guys enjoy :)