Well as I knew nothing about commanding I just assumed the role of the average soldier and kept spamming 'h'. Got into it and bought the game. Haven't really played with the aliens yet, marines have kept me content. 
Now, see, that's the right way to get started, if only the others had all done the same. You should play aliens too, it's a blast.
Pointers: as skulk you get a speed boost by jumping sideways onto a wall, then jumping again to get off it while always facing and moving moving forward. You can use that to move around the map faster and attack marines more effectively as well. Always stay off the floor when you're charging someone, use walls, ceilings and jumps to dodge when someone is shooting at you (or ambush when they're not). Once you close the distance, try to circle strafe around him etc. to keep him confused. It's also often helpful to tap LMB for single bites instead of holding it down, that way you can time it just right when you have him centered.
