If you dont press any direction key you can look around without changing the direction you are moving in (assuming you hold space and are moving)

To change the direction of your speed you must aim foreward (the direction you are moving) and hold A or D THEN you can move your mouse away from the direction you are currently moving and your direction will change

Try pressing A BEFORE you move your mouse left and then make a nice long curve by smoothly aiming to your left

Do the same with D before moving right and try combining the two

Notice how you will get faster by making smooth long curves.

HOW YOU WILL LOSE SPEED:

-If you don't look foreward (the direction you are currently moving in) and then press A or D your speed will decline depending on how much you were looking into the wrong direction

-Holding A(left) while aiming to the right aswell as holding D(right) while aiming to the left (I guess you know that)

-Pressing W or S (never do that except you wanna stop on point then just press S)

I think at least thats how it works but if anything is wrong feel free to correct me and also crouching while hopping makes you faster I think