I ALWAYS use a metronome. From the first note that I play when reading it the first time, to the last. I listen to a recording first and follow along in the music. Then I start working on it after a few times listening.
I break it down measure by measure, and if need be, I break it down beat by beat. I used to do 2-3 measures at a time but I found that in the long run it takes longer. Break it down as small as possible and play it with a metronome slowly. I personally make myself only increase the metronome clicks by 2 beats if it is challenging, 5 beats if it is easy. So 30 would become 32/35 (depending on the music). I also ALWAYS use subdivisions at first. After a while I will stop using subdivisions and will start grouping in larger portions (like 2 beats on the met. for a 4/4 bar, or 1 beat per every 3/4 bar etc).
Practice techniques aside from the metronome: moveable fermata. (Basically hold out the 1st note in a group of 4 16th notes as you play the run, then hold out the 2nd note in a group of 4, 3rd, etc). I change the rhythms, the style, the dynamics. If it's really hard (or I want it to be really smooth and even) I play against the metronome sort of... (on the upbeats) or if the time signature says it has 4 16ths to a beat I regroup them into 3 16ths to a beat (changing my metronome marking) which would put a beat on the 1st 16th of the bar, and the 4th 16th note of the bar (and so on).
I will also take small chunks (like half a beat or so) and play them slowly until I can play them 30+ times correctly without messing up. If I mess up, I start over.
And if all else fails I play it backwards. I play the music from right to left. And if it's still bad.... well... I pack up and call it a day. If I don't I will end up breaking something.
