This is exactly the way I learned to practice riffs in jazz solos. You start at half speed, then slowly increase the speed, but only increase the speed if you

This is exactly the way I learned to practice riffs in jazz solos. You start at half speed, then slowly increase the speed, but only increase the speed if you can play the passage perfectly 3 times in a row at the current speed. It works amazingly well. It also requires persistence and determination, but so does any type of skill that differentiates you from the average person.