Compared to the below method, this method can be done with either a bomb or a bombchu and is a bit faster. To do, get near a ledge and pull out a bomb or bombchu and hold Z. If you're using a bomb, jump off the ledge when the fuse is almost up, for a chu you can jump any time. When you jump quickly press R to shield drop then B for a jumpslash.
To do it buffered, pull out the bombchu and hold Z. Jump off the ledge and buffer to the first or second frame that Link starts moving upwards (both work). On this frame, buffer R for one frame to shield drop the bombchu. Then buffer only B to boost up the the higher ledge.
Compared to the previous method, this method can be done without the shield. To do this, pull out a bombchu and stand about a foot away from the edge of the platform you're standing on. As soon as the bombchu begins to flash rapidly--about 7 flashes--run off the ledge and hit B once you're in the air. The bombchu should explode and boost you to your desired ledge.