The most important part of becoming a skateboarder is owning and equipping the Boston Boarder taunt. This can be obtained via the Mann Co Store, the Marketplace, trading, etc. The reason this is so important is that without it, you cannot become a skateboarder, as you will not have a skateboard. There is not much else to becoming a skateboarder, so it's relatively easy.

The best way to play skateboarder is to prioritize stealth. When skating, skate out of the enemy's line of sight and get behind their lines.
If not sneaking behind enemy lines, it's best to spam voice commands in chat. Top voice commands are "Help!", "MEDIC!", and "Thanks!" Any voice command is viable, however.
It may also help to getting a few RADICAL cosmetics, such as the Backwards Ballcap, Track Terrorizer, etc.

These are small bits of information and things you can do to improve your performance in certain situations.
If you equip the Bonk Helm, Bonk Atomic Punch, Atomizer, and Soda Popper, it can help you pull off a combo with the Bonk branded skateboard for maximum Bonk.
When confronted in a situation against someone shooting at you, despite your skateboarding skills, it may be best to skate behind a wall, stop skating, shoot the opponent in the face when they come around the wall, and then go back to skating.