All games begin with your starting town right next to a gold mine. Night Elf or Undead players may find their beginning mine prepared to use, will not have to worry about Haunting or even Entangling right away, until,the very first Gold Mine collapses. That is right, Gold Mines don't last forever, so you'll be seeking to expand quickly into the early mid-game. Find a second gold mine early, and begin planning to clear the area and enlarge to a second foundation. You also want to watch for your opponent's expansions. If you have two gold mines, and they've only got you, you are going to be in a critical benefit.
To find out where your opponents are enlarging too, though, you will want to spend a while on recon. Sending a starting employee out to learn more about the map is a frequent tactic, but ensure that you replace them quickly to avoid losing out on precious early game resources. Finding out early what sort of force your opponents are constructing allows to construct an effective counter drive.