Spending time at or training at altitude is the best thing. But short of that the best you can do is get to relatively elite level VO2max. The problem with altitude is less oxygen and V02max is probably the best metric to help with that. Norwegian 4x4 sets on rower or bike twice a week in addition to 4-6 hours of zone 2 over several months will really move the needle on this.
Its hard though, and what still kills me is my HRV during sleep is so off that my recovery is crap and that catches up to me no matter how well trained I am.