Run a mass of Nephalem Rifts in a very fast fashion to acquire tons of keys. Best way to do that is running in public groups. Once you did that enough you run medium level, tier 90 and higher Greater Rifts solo successfully by burning through your stack of keys. Tier 90 and above of Greater Rifts always deliver the highest count of Legendary or Set item loot once Rift Guardian is slain. All the while you can push high end 120-130s if you have augments and stats for it.
Also please consider the element of luck here, they can be the dedicated players but finding a Primal that your class would use is at really low odds. Run some bounties in public games to collect some Horadric Crafting material and you’ll just have enough to reforge a few items just enough to reach a Primal if you haven’t found one yourself. Thinking how rare the Primals actually are, you should consider doing more than one task and juggle others, which only a dedicated player could prevail.