Currently aside from just having a good path and taking corners (which means hitting all Rocket Pieces and Energy Boosts by only slightly hitting them and also being very close to hitboxes of rocks but NOT hitting them), there are 2 places which stand out, so we call them strats:

#The Bounce It's the easier one, while on the path for the 5th Rocket Piece just before you can catch it, go left up until you hit a rock and then right to go for the next one. It saves around 5-6 frames (in 30 FPS videos) (0.167-0.200 sec). It is really only useful in Any%.

#Poopsey Skip Named after the player who was the first to record its use. While going for the 7th Rocket Piece it is actually possible to get between 2 rocks surrounding the Rocket Piece. Firstly you got relatively low in the upper left direction and then just left at the end. Too high and you'll bounce off the right rock, too low and the same for lower rock. Sometimes you might bounce off 2 times before finally going through, which still is faster than taking the route above the right rock. It saves about 1.333 sec in Any%, timesave in All Items isn't calculated yet.

#Current Path Current Path is was first recorded in this video, dha's WR (at the date of writing this) 59.217. It looks somewhat like this: https://imgur.com/a/Li5y9Sb