Are you referring to economy picking? d u d, d on the next string when ascending?
If so, what helped me years ago was to just play six notes, focusing on those changes. I found the tension of the A to D or the D to G string the most similar and were the easiest to practice on. Start with 12 14 15 on the A and play 12 14 15 on the D or the same fingerings on the D and G. Mentally for me, when it works, it feels like sweeping arpeggios. I consciously push my hand downwards towards the high E string. I don’t try to focus on the alternate picking of one string, just the gliding motion of the string change, the rest is ‘auto pilot’. You may even simplify it even more by playing 12 13 14 on the D G B E string consecutively, again just focus on the feeling of pushing downwards with the same motion that you use sweeping minor/maj arpeggio shapes.
Another exercise, would be to play an arpeggio, 12 14 15 A string, 14 D string 12 14 G string. Picking d u d, d, d u. The same thing applies, don’t think so much about the first two notes, more about pushing through the 15th fret downwards towards the 14th to the 12th. Play the entire thing a few times, then just the 15 A 14 D 12 14 G a few reps, then the whole thing, back and forth.