You sprint then quickly crouch before jump = sprint then C+Espace for example
Try it ! It’s dumb but it’s fun ! 
You sprint then quickly crouch before jump = sprint then C+Espace for example
Try it ! It’s dumb but it’s fun ! 
Longjump is certainly useful, and not just for trickjumps.
-Use it to quickly leap across short distances, minimizing damage taken crossing gaps for example.
-Longjump to cover to escape an engagement, or into a Health Station or Medpack to get your heals.
-Melee kills can definitely use a Longjump to close in on the enemy before slice-and-dice.
-As Bushwhacker, if I know where my Turret’s going to be, I Longjump the last short bit to that spot so I can get that Turret up just a little bit quicker.
Do be warned: you’ll get a small but certainly noticeable speed penalty for a couple of seconds after landing, or a “sitting duck” in layman’s terms.