Practice this specific sequence in the lab: Hit Up + B simultaneously, and then immediately roll the control pad to due right. Pikachu should zip over to the right. Make sure you're holding right until Pika moves. Repeat until it's consistent. It's not that fast of a motion if you're used to playing other fighting games, but I can see how it can be a challenge for a newer player... especially considering how the 3DS circle pad doesn't have any ridges. I want ridges on it so bad, but it didn't take me that long to land QA consistently on the 3DS, since I've played Monster Hunter and Kid Icarus on the thing (I had to super-glue the rubber back on before I traded it in to GameStop, haha).
The second input is just a matter of getting used to how long it takes for Pika to zip over before you should hold the next direction. So, Up+B, roll to the right, Pika zips over, hold down+right, Pika zips over again. Most Pika players have practiced to the point where they can perform the move without even looking or hearing the sound, so it's sometimes challenging to remember how much of a struggle it used to be.