Shield drop is one of the simplest techniques. With any grabbable object in Link's hand (bush, bomb, rock etc.), press R to bring out his shield and the object will fall straight to the ground.
Thats all. This is a much faster way to drop items than throwing or placing them with A and can be done in mid-air while pressing Z, but it also has some other uses.
Backflip, pull out a bombchu and press R to shield drop it. It will instantly explode. This can be done with a sidehop too but the timing is much more strict. This is also an important part in Bomb Hovering.
Another way to make a bombchu explode instantly. While walking forward, hold Z and press R to shield drop it then quickly press B while still holding forward. Your sword should hit the chu making it explode. If you do this as adult you must let go of Z before pressing B because a simple forward thrust will go over the chu and not hit it.
Get near a ledge and pull out a bomb or bombchu. If you are using a bomb, jump off the ledge when the fuse is almost up; for a bombchu you can jump any time. When you jump, quickly press R to shield drop then press B for a jumpslash. This gets slightly more height and distance than a normal damage-boosted jump which is required for some tricks such as Shadow Early.