The best way to get Hilton Diamond status is by having the Hilton Honors Aspire Credit Card. Diamond Tier status comes complementary with this card.
You can also reach Diamond status by spending $40,000 a year on either the Hilton Honors American Express Surpass Card or Hilton Honors American Express Business Card.
Lastly, if you don't want to deal with credit cards, you can get the status by completing 30 stays, or 60 nights or earning 120,000 Hilton points in one calendar year.