2NDayzi's profile

first charge a blue miniturbo as normal while holding up, you can do this in either direction

after that, continue to do a normal drift in the same direction as the previous drift, but this time, while still holding down the drift key, let go of up while mid-drift and press down, then let go of down and press up again, then let go of up and press down again and repeat

if done right you should be driving in a semi-straight line

keep repeating this motion until RIGHT after the sparks under your kart turn orange (this will charge a Super Mini Turbo), then briefly let go of the drift key to release the miniturbo before continuing to do the same thing you were doing
use this to chain Super Mini Turbos over and over again

if I were you I would practice RDing in both directions as well as where to switch directions optimally, watch a lot of time trials ghosts on certain tracks and eventually when you become more killed at the game you will be able to kinda get a feel for the tracks themselves and how to run them. I recommend starting with learning GBA Bowser Castle 1 rather than Figure 8 Circuit because it's still a very easy track but it's more representative of the other tracks and it kinda gives you a feel for what I mean

note that when you switch directions you don't have to and shouldn't recharge the first MT, I included it in my description because it gives you an acceleration boost. it's only when you come to a complete stop (e.g. when you fall off the track or get hit by a blue shell) that you'd need to charge a blue miniturbo