By popular demand!

1. Select all your overlords
2. Tell them to move to a location beyond your enemy's army
3. When the time is right, press "D" and select the overlord you want to drop with. Repeat the process with each overlord. ie. D, click, D, click, D, click, D, click...
4. Watch your banelings commit hari kari.

TIP #1: Time your overlords to move in JUST after yourmeaty ground forces so your overlords don't die and lose precious cargo!
TIP #2: Include several empty overlords as well to fool your enemy. If he chooses to focus fire your overlords, he'll end up killing empty ones and your ground forces can mop him up!

Enjoy,

PsY