The steep drop near the race’s start is obviously much more dangerous with opponents in the mix. There’s bound to be plenty of jostling at the race’s start, so take steps to protect yourself; stay near the center of the track to ensure you survive early collisions.
The cavern is a great place to use a Green Shell—particularly if you have one on the first lap. If you have a Banana, drop it near the cavern exit; the narrow passage makes it much harder to dodge. Your opponents are likely to use these tactics against you, so use the Touch Screen to check for items hidden around blind corners.
When you can’t boost through the grass, make sure you perform a jump boost from the ramp in the path. It’s not nearly as effective as the shortcut, but it’s your best option when you don’t have a Mushroom.
The climb back up the mountain is another great spot to drop Bananas. If you have one, try to place it just after one of the dash panels along the path’s center. Most racers will cross over both of these as they boost up the path, so you have an excellent chance of catching someone in your trap.