Null Jump
When performing a walljump without any momentum you gain considerably more height than normal. This phenomenon is called a null jump. Null jumps give you the same height as looking straight up when performing a jump.
Execution
Null jumps are arguably the easiest thing to pull off. Simply stand next to a wall and do a normal jump. The only thing you need to pay attention to is not gaining any horizontal speed when attaching to the wall. This just means to jump off the wall quickly.
Pros and Cons
The quick and easy gain of height is the major advantage of null jumping. However this can also be achieved by simply looking straight up during the jump without having to sacrifice your speed. Therefore null jumps are generally not recommended.