Either just grind for the skateboard or keep playing BM.

• The skateboard is used for going super fast.
  
• It CAN wall jump, but bounces off and keeps going.
  
• The skateboard is used in the grenade slot.

Another thing is - go in the shooting range, get familiar with the area and do a time trial with ONLY 1 PISTOL - no changing weapons - and a skateboard. If you get a time that is 1:30 or less, you're good.

Now, this section doesn't SPECIFICALLY have a lot of tricks.

What CAN have a lot of tricks, though, is the fun section. Just one section below.

• If you get stuck in some corner with some random dude about to shoot you, IMMEDIATELY shoot ONE bullet to ricochet him back and IMMEDIATELY: 1. Roll away from him. 2. The FIRST frame you get a chance, switch into your skateboard.
  
• Wall jumping is incredibly useful. Backed against the wall? No problem! Run to the wall with your skateboard, then wall jump. Dismount your skateboard, then KILL THAT FRIGGER!

Maybe you're not quite fond of being all "m45t3r pr0" and whatnot.

So, here's some tricks.

• You can infinite wall jump if you do it at certain times.
  
• You can spam the W button and have fun while saying the lines (SICK! ILL! RADICAL! SICKNASTY!)
  
• YOU CANNOT FIRE WEAPONS. So basically on a skateboard basically means you're now officially in safe/pacifism mode.

Well, one more than the last guide.