Sell Fallen Sword Points or other items to get 2,500,000 gold and go to the Auction House. Select the "Special" tab and look through that section until you find a "Supreme Potion of Doubling". Bid 800K gold for each one that you find. You should win that auction. Collect your potions and use them to get a buff level of 450. This will multiply the amount of experience you earn to about x8.