Well, umm, the first thing you'll want to pay attention to is both you and your opponent's percentages, for as you know, ANYTHING can happen in a lucario ditto lol. Generally, the one who starts off losing is the one that ends up winning due to the aura kick'n in. This is because a player will naturally start playing more defensive when at a higher percentage in order to, you know, not lose that stock! Their opponent, though, doesn't understand this, and will continue to play offensive until they finally begin to lose their lead that they had first started out with. Eventually, they're going to lose that stock due to aura and will then have to find a way to kill Lucario without any aura of their own, and then THAT Lucario will end up gaining aura because he/she couldn't kill the OTHER Lucario without taking a lot of damage themselves because of the OTHER Lucario already having a ridiculous amount of aura from the start, and then-
....You see what I mean? Lol
Here's a good example of what I'm talking about. Pay close attention to both player's percentages and how the match plays itself out with all of the aura flying around the place.
So what do I propose you do? Play more cautiously is all. All dittos generally work out the same, as in the more patient player between the two will come out the victor. Instead of just blindly approaching him with a Fair or throwing out Fsmashes everywhere, understand that you're playing the same kind of character as your opponent. Don't you think that they would also like to blindly approach you with a Fair or attempt to hit you with at least ONE Fsmash? Play safe, ESPECIALLY when the other Lucario has some aura going and is looking for a comeback. Always remind yourself that YOU still have the lead.
Hope I helped any :)