Double: simply jump in mid air
Duck: duck in the middle of your jump to get extra clearenceRamp: jump after running up an encline
Rocket: simply fire at the ground under your feet & jump, it couldn't be any easier! You can also fire at the ground behind you or at the wall you are next to while in the air for farther &/or higher jumps.
Grenade: fire a grenade down, wait for it & jump with the detonation of the grenade, this has the same results as rocket jumping, but it is much harder.
Mine: detonate a mine that's next to or under you while jumping.
Bunny hopping: jump repeatedly while running to gain more speed, either by doing a speed jump(foward+strafe+ move mouse in the same direction as the strafe)doing it until you gradually gain bigger speed, or using an explosion to go MUCH faster.
Enemy: allow at least one enemy to hit you, which won't get you the explosive jump results(unless someone launches one at you)but can be helpfull if there is a platform or gap that is a bit to tall or wide for you to jump to normally, but not if you let someone shoot you, just be sure to get away &/or fight back, because they ain't welcoming you to the match!(also usable in some platformers such as castlevania & super mario bros 2)
Recoil boost: some weapons have recoil on the player who fired it while in mid air & as such can be used in a similar fashion to explosive jumping.
Strafe: while jumping, strafe by pressing an arrow key & moving your mouse in the exact same direction.
Combo: fire a rocket at your feet when the grenade under your feet explodes & jump, you'll get much better results, but you'll pay alot more health(you can combine other explosives too)
Explosive jumps can also be done when invincible to avoid taking damage
Glitch: do something weird to make yourself go higher & farther