Our team really likes to do the Roller Coaster in the stands.
Video evidence here.
Wearing coordinating t-shirts is also really important (for regional and for every single event your team attends).
Having constant positive attitudes when dealing with other teams is also important.
The conversation with the judges as they walk around on Thursday and Friday also factor into the decision. Discuss what makes your team awesome and full of spirit when talking with the judges.
Handing out SWAG is important. We like to handout wristbands but buttons, stickers, wood decals, necklaces, and a million other things are handed out as well.
More examples are found here.
There are just a ton of stuff that factor into the Spirit Award (just like every other award). Appearance, attitude, cheers, signs, swag, all of it adds up.