The
deck is the
board part of the skateboard . Ask yourself, "what kind of skateboarding do I think I'll do most?"
Transition / Vert
Are you looking forward to mostly skateboarding at the skatepark, vert ramps or pools? Most of this type of skateboarding uses a wider board, something wider than 8" (8.25" or 8.38" are good choices).
Street / Technical
Do you see yourself skateboarding around a school yard, the street in front of your friend's house, at a skate plaza, or downtown? Most of this type of skateboarding involves flip tricks or grinds. These types of skateboarders are usually most comfortable with a deck 8" wide or smaller (7.5", 7.75" or 8" are good).
Anything much wider can make it hard to do technical tricks.
Both / All Terrain
If you want to master both street and vert styles (not a bad idea at all), then you should look at a deck that's right about in the middle sizes. An 8" deck would be a good choice. If you find yourself doing more street or vert, you might want to adapt your deck later. A wider skateboard makes ramps easier to ride but flip tricks harder, where a more narrow skateboard makes flip tricks easier but gives a lot less stability on a ramp!
Cruising
If you're looking to use your board as mainly a means of transportation (cruising around town, across campus, or bombing down hills), then the bigger the board the more balance and control you'll have. You might even want to look at getting a long board.