This is the best method to gain height and length.
By placing a bomb on the floor and backflipping twice, you can then perform a shield jump and land on the bomb with your shield. Right as you land on it, mash jump. You'll jump off of the bomb, and if you hit the bomb on the right spot, you'll get a lot of height.
Another method consists on throwing a square bomb, fronthopping once and then shield jumping, as opposed to the two backflips method.
In the air and for extra height, you can unequip your shield and detonate the bomb.
This is an example of one of the best jumps you can get.