Dark templars are one of the most fearsome units new to Starcraft from Broodwar. Delivering 40 damage witht their blades make them very good strikers. They automatically kill marines, ghosts and zerglings with just one strike. Use dark templars with care because their health is fairly low. Use the element of surprise, if your enemy knows you are using dark templars, then you might as well not use them anymore.
Upgrade ground weapons because they give a great +3 bonus. When combining dark templars with other units, send them in first followed by zealots, then dragoons then templars or reavers. The dark templar will deal a huge damage, zealots fininsh them off and the others do the most trashing to the survivors.

• On the 8th probe, build a pylon.
• On the 9th probe, build a gateway and assimilator.
• Build 2 probes, minerals.
• Build 12th probe then gas, two existing probes on gas.
• Build cybernetics core and zealot.
• Two more probes, minerals.
• Build another pylon, citadel of adun and another probe.
• Train another zealot.
• Try scouting the map for enemy activity.
• Build pylon and templar archives and 2nd gateway.
• Build 2 probes and pylon.
• Pump those dark templars and zealots...