Don't camp. Wario hinders camping with his bike very well. He lacks range on his moves, but his aerial DI is insane. Ftilt to space him if he's approaching through shorthops. If he's approaching from above, just move away or something. You don't want to go against his dair if at all possible. If he's grounded, space with fsmash. He has super armor on his fsmash, so it's going to do you no good ftilting him when he can protect himself with SA frames and kill you. Save ftilt for when he's in the air.
Avoid the uair. Always. it has very deceptive range, and deals a helluva lot of damage. Waft is stupid good on killing your recovery. If he's chasing you and you're forced to extreme speed, expect to be killed by the lovely overpowered move that is The Waft. Fsmash and ftilt kill as well, but you shouldn't have a problem spacing them with fsmash.
Wario pressures very well. Once he's inside it's very difficult to get him off.
EDIT: And as Nessbounder said, try getting him off his bike if he pulls it out. If he does it on stage, sh aerial him. From there keep him away from the bike and pressure him to the ledge as hard as you can. If he pulls out the bike while he's recovering, you can easily predict when he jumps off the bike and you can knock him right back out. If he's forced to uB, dair it. It has like, no vertical hitbox.