It's going to take something subversive. Direct assault brings too many heavyweights into the game. It'd have to be something like a MU braintrust of Thanos, Doom, Grandmaster, Reed, High Evolutionary, Apocalypse, etc. finding a way to covertly mind control or weaponize most of the DCU's non-meta population to gain an overwhelming numbers advantage, then after springing a trap and mind controlling a majority of the universe unleashing hell on the people able to resist with a giant stockpile of Cosmic Cubes and the Infinity Gauntlet.
I'd bide my time and do a lot of reconnaissance using Skrulls and telepaths, abducting a member of the various non-meta races of the DCU for genetic evaluation and experimentation. I'd then have Thanos, Apocalypse, High Evolutionary, Mr. Sinister, and members of Weapon Plus create a techno-organic virus that infects non-meta humanoids and rewrites their DNA to become the Thanos Clones from Infinity Abyss, the Super Skrull variants from Secret Invasion, the Harbinger of Apocalypse, and Weapon XVs upon activation (it would lie dormant until a signal activated). I'd then employ legions of Skrulls to impersonate the natives of various planets in the DCU and spread the virus throughout their food and water supply as well as have an airborne variant. Once that phase is complete I'd extract the Skrulls and send in Ultron and his armies along with the Phalanx and Technarchy to make it appear as a typical alien robot invasion (and also to remove the possibility of a telepath picking up this was all part of a bigger plot). When the native metas engage the Ultrons the virus would be activated and each planets non-meta population becomes part of my army and we'd massacre the native metas.