So I've been playing for a few years and one thing I want to get down is repeat riff solos that are common in metallica and iron maiden, or thrashy stuff in general. I understand it when I read it, but my fingers stuggle between the high b and e strings and can't make it sounds smooth. A good example is master of puppets solo. Any tips for those who've practiced thrash solos?
Like anything, take the phrase at a much slower pace while working at making it more efficient and clean. Be sure that you can play it slower before you play it faster. If your technique is clean at slower tempos, it'll make it easier to do it faster.

If you have TuxGuitar or GuitarPro, you can easily open up the tab of the song, put on a metronome, and loop the phrase in question.
Skip the username, call me Billy