Pick any scale or run that you wish - it doesn't matter, but what does matter is that you coordinate the moment that your pick hits the string with the moment that you press behind the fret. Not before, or after you have started to go to the next note. Sounds obvious, but you might be trying to run before you can walk. Play a C major scale for example, and play it very, very slowly, perhaps 1 note every 2 seconds. Let each note go the whole duration of the period. Then fret the next note. Do this slow motion playing for maybe 10 minutes. If you make any single mistake, focus on that particular section, practice it and then start over. When you can do that successfully, get a metronome.