Originally Posted by osiris
Whilst repetition will help, if you're doing it wrong, all you're doing is programming in a bad approach. The practice that you do with a metronome requires that you're doing it right in the first place. Otherwise, you're just making an uphill battle for yourself.
Whatever the part is, slow it down. Preposterously slow at first.
With your picking hand:
Experiment with your hand position on the phrase, pay a lot of attention to how your holding the pick, how tightly you're holding it, what dynamic control you have with it (but don't worry about overall dynamics yet), how your arm is sitting, how close to the bridge, the angle your hand is, where on the string you're picking.
With your fretting hand:
Pay attention to the fingering you're using, how far away from the fretboard your fingers are moving, are certain fingers a bit more stiff (oo-la-la) than others, is your pinky doing that hilarious shrivelled up thing, are you arching your hand too far or too little, is your thumb too high/low on the neck.
All of those details frequently get overlooked in favour of simply running through the exercise and concentrating on speed, and maybe volume/dyamics and articulation. Those are all great things to concentrate on, but you need to get the foundations solid to work on that stuff.
Really be strict and dissect everything you're doing. Go to town on it. It's actually a very cool exercise in mindfulness (bringing one’s complete attention to the present experience on a moment-to-moment basis
) and can be very enjoyable. Once you find a mechanically comfortable way to play the phrase, and one that fits in with your playing style, you can work on developing the speed, which will now be much easily attained.