Do your regular build order and all that bull shit, but once you can, start pumping out ghosts, battle cruisers, and valkyries. Have the ghosts lockdown any machine pain in the ass, and make sure you have medics to back up the ghosts. The ghosts can help take out ground and air, likewise for the cruisers, while the valkyries protect those bitch ass expensive cruisers from being harrassed by air units. Make sure to upgrade the weapons for both the ghosts and the air units, for ghosts don't forget to researh lockdown. If your playing against zerg or terran, research cloak because their detectors can easily be tooken out. Yamato Cannon for the bc's is helpful if you want to save your guys some trouble killing guard towers. Make sure you have at least 10 valkyries for them to be effective since they only work well in groups. researching extra energy for the ghosts would be helpful, but won't stop you from using lockdown twice, it'll just make their energy recover faster, well obviously you knew that.

CreepColony's Opinion: Ghosts are definetely not for attacking with their wimpy 10 concussive damage weapon. Maybe good for taking out non-upgraded small units, but in general pretty useless. Also, always be sure to bring in a few detectors.