Don't be afraid to sacrifice attack for "Neo-Spacian Grand Mole" by using it first and Summoning this card next turn, especially if there is a "Gorz the Emissary of Darkness" as your backup; this monster would have a formidable 3600 ATK when using those other 2 cards.
Combine "Dark Gaia" with "Ojama Trio". Since it forces all of your opponent's monsters into Attack Position, they will have no choice but to take the full ATK of "Dark Gaia".
Use "Dark Fusion" to Summon this card, then use "Dark Calling" on the same Fusion Materials that was used from the Graveyard to Summon another identical "Dark Gaia".
When there is a good Fusion Materials on your field; use "Torrential Tribute", and then "Dark Calling". Then attack your opponent directly with "Dark Gaia", easily leading to a finishing blow.
"Number 30: Acid Golem of Destruction" can be used, currently the 4th-strongest Rock-Type, as a Fusion Material for this monster to get all of its ATK with none of its drawbacks, and without having to fill your Main Deck with monsters just for the purpose of fusing into this. However, it will first have to be destroyed, as it prevents yourself from Special Summoning while its under your control.
Fortunately, as the "Acid Golem" is a powerful monster in its own right, your opponent may destroy it to protect themselves, giving yourself further advantage over them.
For your Fiend-Type monster, a "Tour Guide From the Underworld" (perhaps used as Xyz Material for the "Acid Golem" in the first place) can be utilized or, for maximum efficiency with a highly-usable Fiend-Type monster, "Gorz the Emissary of Darkness" to give yourself a 5700 ATK "Dark Gaia".
Use Ritual Monsters in your Deck, so that their high ATK can be used for the Fusion of "Dark Gaia", or if this option is not available during your turn, Ritual Summons can still happen. Beware that currently there are no Rock-Type Ritual Monsters.
Use the "Gogogo" monsters along with Fiend-Type monsters with high ATK like "Darkness Neosphere" to make a strong "Dark Gaia" along with enhancing the ability to use both "Dark Fusion" and "Dark Calling" as well as the ability to easily run Rank 4 Xyz Monsters in your Deck. "Gogogo Goram" is a big help to get "Gogogo" monsters into your Graveyard to use with "Dark Calling", and use "Gogogo Giant" to Special Summon those sent "Gogogo" monsters and fuse them using "Dark Fusion".
List of Fiend and Rock Type monsters (in order of ATK):